Method for producing exhaust gas purifying catalyst

ABSTRACT

To provide a method for industrially efficiently producing an exhaust gas purifying catalyst containing a perovskite-type composite oxide which is stable and has a less reduced specific surface area and is also effectively prevented from decreasing in its catalytic performance even in endurance in high temperature oxidative reducing atmospheres, a pre-crystallization composition containing elementary components constituting a perovskite-type composite oxide containing a noble metal is prepared, is mixed with a powder of theta-alumina and/or alpha-alumina to prepare a mixture, and the mixture is heat treated. Thus, the resulting perovskite-type composite oxide supported by the powder of theta-alumina and/or alpha-alumina can keep its thermostability at a sufficient level thereby to effectively prevent the catalytic performance from decreasing. This method can industrially efficiently produce the exhaust gas purifying catalyst.

TECHNICAL FIELD

The present invention relates to a method for producing an exhaust gaspurifying catalyst. More specifically, it relates to a method forproducing an exhaust gas purifying catalyst containing a perovskite-typecomposite oxide for use as an exhaust gas purifying catalyst.

BACKGROUND ART

Perovskite-type composite oxides each supporting a noble metal such asPt (platinum), Rh (rhodium), or Pd (palladium) have been known asthree-way catalysts which can simultaneously clean up carbon monoxide(CO), hydrocarbons (HC), and nitrogen oxides (NOx) contained inemissions. Such perovskite-type composite oxides are represented by ageneral formula: ABO₃ and enable the supported noble metal tosatisfactorily exhibit its catalytic activity.

These perovskite-type composite oxides, however, undergo grain growth,thereby to have a decreased specific surface area at a high temperatureof about 1000° C. The resulting catalysts can only contact with exhaustgas components in a shorter time and exhibit remarkably decreasedcatalytic performance in an operating environment at a high spacevelocity as in the case of exhaust gas purifying catalysts forautomobiles.

Accordingly, various attempts have been proposed to increase theirthermostability by allowing such a perovskite-type composite oxide to besupported by a thermostable composite oxide containing Ce (cerium)and/or Zr (zirconium) and, for example, the use of Ce_(0.8)Zr_(0.2)O₂and Ce_(0.65)Zr_(0.30)Y_(0.05)O₂ as the thermostable composite oxide hasbeen proposed in Laid-open (Unexamined) Patent Publications No. Hei5-31367, No. Hei 5-220395, No. Hei 5-253484, No. Hei 6-210175, No. Hei7-68175, and No. Hei 7-80311.

Laid-open (Unexamined) Patent Publication No. Hei 5-31367 discloses themethod comprising adding an aqueous solution containing nitrates ofmetal constituting a perovskite-type composite oxide in a predeterminedstoichiometric ratio to thermostable composite oxide powders, drying themixture at about 100° C. for 5 to 12 hours and further baking at 700° C.to 800° C. for 3 to 10 hours, thereby to support the perovskite-typecomposite oxide by the thermostable composite oxide.

Even the perovskite-type composite oxide is supported by thethermostable composite oxide containing Ce and/or Zr, however, it isdifficult to secure sufficient thermostability of the perovskite-typecomposite oxide.

DISCLOSURE OF INVENTION

Accordingly, an object of the present invention is to provide a methodfor industrially efficiently producing an exhaust gas purifying catalystcontaining a perovskite-type composite oxide which is stable, has a lessreduced specific surface area and is effectively prevented fromdecreasing in its catalytic performance even in endurance in hightemperature oxidative-reducing atmospheres.

The method for producing an exhaust gas purifying catalyst of thepresent invention comprises the steps of preparing a pre-crystallizationcomposition containing elementary components the elementary componentsconstituting a perovskite-type composite oxide containing a noble metal;mixing the pre-crystallization composition with a powder oftheta(θ)-alumina and/or alpha(α)-alumina to prepare a mixture; andsubjecting the mixture to heat treatment.

In the method of the present invention, the perovskite-type compositeoxide is preferably represented by the general formula (1):AB_(1-m)N_(m)O₃  (1)wherein A represents at least one element selected from rare earthelements and alkaline earth metals; B represents at least one elementselected from Al and transition elements excluding the rare earthelements and noble metals; N represents at least one noble metal; and mrepresents an atomic ratio of N satisfying the following relation:0<m<0.5.

N in the general formula (1) is preferably at least one selected fromthe group consisting of Rh, Pd, and Pt.

The perovskite-type composite oxide represented by the general formula(1) is preferably at least one selected from the group consisting of Rhcontaining perovskite-type composite oxides represented by the followinggeneral formula (2), Pd containing perovskite-type composite oxidesrepresented by the following general formula (3), and Pt containingperovskite-type composite oxides represented by the following generalformula (4):A_(1-p)A′_(p)B_(1-q)Rh_(q)O₃  (2)wherein A represents at least one element selected from La, Nd, and Y;A′ represents Ce and/or Pr; B represents at least one element selectedfrom Fe, Mn, and Al; p represents an atomic ratio of A′ satisfying thefollowing relation: 0≦p<0.5; and q represents an atomic ratio of Rhsatisfying the following relation: 0<q≦0.8,AB_(1-r)Pd_(r)O₃  (3)wherein A represents at least one element selected from La, Nd, and Y; Brepresents at least one element selected from Fe, Mn, and Al; and rrepresents an atomic ratio of Pd satisfying the following relation:0<r<0.5,A_(1-s)A′_(s)B_(1-t-u)B′_(t)Pt_(u)O₃  (4)wherein A represents at least one element selected from La, Nd, and Y;A′ represents at least one element selected from Mg, Ca, Sr, Ba, and Ag;B represents at least one element selected from Fe, Mn, and Al; B′represents at least one element selected from Rh and Ru; s represents anatomic ratio of A′ satisfying the following relation: 0<s≦0.5; trepresents an atomic ratio of B′ satisfying the following relation:0≦t<0.5; and u represents an atomic ratio of Pt satisfying the followingrelation: 0<u≦0.5.

Theta-alumina and alpha-alumina is preferably represented by thefollowing general formula (5):(Al_(1-g)D_(g))₂O₃  (5)wherein D represents La and/or Ba; and g represents an atomic ratio of Dsatisfying the following relation: 0≦g≦0.5.

In the method of the present invention, the pre-crystallizationcomposition is preferably prepared by mixing a solution containingalkoxides of elementary components constituting the perovskite-typecomposite oxide excluding at least one noble metal with a solutioncontaining an organometal salt of at least one noble metal.

In the method of the present invention, the organometal salt of thenoble metal is preferably a noble metal complex comprising at least oneof a β-diketone compound or β-ketoester compound represented by thefollowing general formula (6) and/or a β-dicarboxylic ester compoundrepresented by the following general formula (7):R³COCHR⁵COR⁴  (6)wherein R³ represents an alkyl group having 1 to 6 carbon atoms, afluoroalkyl group having 1 to 6 carbon atoms or an aryl group; R⁴represents an alkyl group having 1 to 6 carbon atoms, a fluoroalkylgroup having 1 to 6 carbon atoms, an aryl group or an alkyloxy grouphaving 1 to 4 carbon atoms; and R⁵ represents a hydrogen atom or analkyl group having 1 to 4 carbon atoms,R⁷CH(COOR⁶)₂  (7)wherein R⁶ represents an alkyl group having 1 to 6 carbon atoms; and R⁷represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms.

The method for producing a catalyst composition of the present inventioncomprises the steps of preparing a pre-crystallization compositioncontaining elementary components, the elementary components constitutinga perovskite-type composite oxide containing a noble metal; mixing thepre-crystallization composition with a powder of theta-alumina and/oralpha-alumina to prepare a mixture; and subjecting the mixture to heattreatment.

According to the method for producing an exhaust gas purifying catalystof the present invention, since the perovskite-type composite oxide issupported by the powder of theta-alumina and/or alpha-alumina, theresulting exhaust gas purifying catalyst containing a perovskite-typecomposite oxide is stable and has a less reduced specific surface areaand also can keep sufficient thermostability of the perovskite-typecomposite oxide even in endurance in high temperature oxidative reducingatmospheres, thereby to effectively avoid the catalytic performance fromdecreasing.

BEST MODE FOR CARRYING OUT THE INVENTION

The method for producing an exhaust gas purifying catalyst of thepresent invention is a method comprising supporting perovskite-typecomposite oxides containing a noble metal by theta-alumina and/oralpha-alumina thereby to produce an exhaust gas purifying catalyst.

The perovskite-type composite oxide containing a noble metal for use inthe present invention are composite oxides each having a perovskitestructure represented by the general formula: ABO₃ and comprising anoble metal as a constituent (excluding composite oxides wherein thenoble metal was supported by the perovskite-type composite oxide later),and are also represented by, for example, the following general formula(1):AB_(1-m)N_(m)O₃  (1)wherein A represents at least one element selected from rare-earthelements and alkaline earth metals; B represents at least one elementselected from Al and transition elements excluding rare-earth elementsand noble metals; N represents one or more noble metals; and mrepresents an atomic ratio of N satisfying the following relation:0<m<0.5.

In general formula (1), examples of the rare-earth elements representedby A include Sc (scandium), Y (yttrium), La (lanthanum), Ce (cerium), Pr(praseodymium), Nd (neodymium), Pm (promethium), Sm (samarium), Eu(europium), Gd (gadolinium), Tb (terbium), Dy (dysprosium), Ho(holmium), Er (erbium), Tm (thulium), Yb (ytterbium), and Lu (lutetium).

Examples of the alkaline earth metals represented by A include Be(beryllium), Mg (magnesium), Ca (calcium), Sr (strontium), Ba (barium),and Ra (radium). These alkaline earth metals can be used alone or incombination.

Examples of the transition elements represented by B excluding therare-earth elements and the noble metals in general formula (1) includeelements having atomic numbers of 22 (Ti) through 30 (Zn), atomicnumbers of 40 (Zr) through 48 (Cd), and atomic numbers of 72 (Hf)through 80 (Hg) in the Periodic Table of Elements (IUPAC, 1990) exceptfor the noble metals having atomic numbers of 44 through 47 and 76through 78. These transition elements can be used alone or incombination.

Preferred examples of B, i.e., Al and the transition elements excludingthe rare-earth elements and the noble metals, include Ti (titanium), Cr(chromium), Mn (manganese), Fe (iron), Co (cobalt), Ni (nickel), Cu(copper), Zn (zinc), and Al (aluminum).

Examples of the noble metal represented by N in the general formula (1)include Ru (ruthenium), Rh (rhodium), Pd (palladium), Ag (silver), Os(osmium), Ir (iridium), and Pt (platinum), of which Rh, Pd, and Pt arepreferred. These noble metals can be used alone or in combination.

The atomic ratio m satisfies the relation: 0<m<0.5. Namely, N is anessential component, the atomic ratio of N is less than 0.5, and theatomic ratio of B is 0.5 or more.

In the present invention, N in the general formula (1) is preferably atleast one selected from the group consisting of Rh, Pd, and Pt.

More specifically, if the noble metal is Rh, Rh containingperovskite-type composite oxides represented by the following generalformula (2) are preferably used as the perovskite-type composite oxide:A_(1-p)A′_(p)B_(1-q)Rh_(q)O₃  (2)wherein A represents at least one element selected from La, Nd, and Y;A′ represents Ce and/or Pr; B represents at least one element selectedfrom Fe, Mn, and Al; p represents an atomic ratio of A′ satisfying thefollowing relation: 0≦p<0.5; and q represents an atomic ratio of Rhsatisfying the following relation: 0<q≦0.8.

If the noble metal is Pd, Pd containing perovskite-type composite oxidesrepresented by the following general formula (3) are preferably used:AB_(1-r)Pd_(r)O₃  (3)wherein A represents at least one element selected from La, Nd, and Y; Brepresents at least one element selected from Fe, Mn, and Al; and rrepresents an atomic ratio of Pd satisfying the following relation:0<r<0.5.

If the noble metal is Pt, Pt containing perovskite-type composite oxidesrepresented by the following general formula (4) are preferably used:A_(1-s)A′_(s)B_(1-t-u)B′_(t)Pt_(u)O₃  (4)wherein A represents at least one element selected from La, Nd, and Y;A′ represents at least one element selected from Mg, Ca, Sr, Ba, and Ag;B represents at least one element selected from Fe, Mn, and Al; B′represents at least one element selected from Rh and Ru; s represents anatomic ratio of A′ satisfying the following relation: 0<s≦0.5; trepresents an atomic ratio of B′ satisfying the following relation:0≦t<0.5; and u represents an atomic ratio of Pt satisfying the followingrelation: 0<u≦0.5.

The theta-alumina for use in the present invention is a kind ofintermediate (transitional) alumina until it is transferred toalpha-alumina, and has a theta phase as its crystal phase. Thetheta-alumina can be prepared, for example, by heat-treating acommercially available active alumina (gamma-alumina) at 900° C. to1100° C. in the atmosphere for 1 to 10 hours.

The theta-alumina is available, for example, by heat-treating SPHERALITE531P (a trade name of a gamma-alumina produced by PROCATALYSE) at 1000°C. in the atmosphere for 1 to 10 hours.

The alpha-alumina for use in the present invention has an alpha phase asits crystal phase and includes, for example, AKP-53 (a trade name of ahigh-purity alumina produced by Sumitomo Chemical Industries Co., Ltd.).

Such an alpha-alumina can be prepared, for example, by an alkoxideprocess, a sol-gel process, or a coprecipitation process.

At least one of theta-alumina and alpha-alumina for use in the presentinvention may comprise La and/or Ba. Namely, one represented by thefollowing general formula (5) is preferably used:(Al_(1-g)D_(g))₂O₃  (5)wherein D represents La and/or Ba; and g represents an atomic ratio of Dsatisfying the following relation: 0≦g≦0.5.

D represents La and/or Ba, and the atomic ratio of D represented by granges from 0 to 0.5. Namely, La and/or Ba is not an essential componentbut is an optional component which may be contained optionally, and theatomic ratio thereof is, if contained, 0.5 or less. If the atomic ratioof La and/or Ba exceeds 0.5, the crystal phase may not maintain itstheta phase and/or alpha phase.

The theta-alumina and/or alpha-alumina is allowed to comprise La and/orBa, for example, by appropriately controlling a baking temperature in aproduction process using aluminum oxide and a salt or alkoxide of Laand/or Ba by a conventional method. Alternatively, the theta-aluminaand/or alpha-alumina comprising La and/or Ba can be obtained, forexample, by impregnating theta-alumina and/or alpha-alumina with asolution of a salt of La and/or Ba, followed by drying and baking.

At least one of theta-alumina and alpha-alumina has a specific surfacearea of preferably 5 m²/g or more, or more preferably 10 m²/g or more.In particular, theta-alumina has a specific surface area of preferably50 m²/g to 150 m²/g, or more preferably 100 m²/g to 150 m²/g. Aplurality of theta-alumina and/or alpha-alumina having different atomicratios of La and/or Ba can be used in combination.

The amount of at least one of theta-alumina and alpha-alumina to supportthe perovskite-type composite oxide is not specifically limited and is,for example, 0.5 parts to 20 parts by weight, and preferably 0.5 partsto 10 parts by weight, to 1 part by weight of the perovskite-typecomposite oxide. If the amount of at least one of theta-alumina andalpha-alumina is less than the above-specified range, theperovskite-type composite oxide may not be sufficiently effectivelydispersed and may fail to prevent grain growth in an atmosphere of hightemperature. A proportion of at least one of theta-alumina andalpha-alumina exceeding the above-specified range may invitedisadvantages in cost and production.

The method for producing an exhaust gas purifying catalyst of thepresent invention comprises preparing a pre-crystallization compositioncontaining elementary components, the elementary components constitutinga perovskite-type composite oxide containing a noble metal; mixing thepre-crystallization composition with a powder of theta-alumina and/oralpha-alumina to prepare a mixture; and subjecting the mixture to heattreatment. This allows the pre-crystallization composition tocrystallize, thereby to allow the theta-alumina and/or alpha-alumina tosupport the perovskite-type composite oxide containing a noble metal.

More specifically, such a method can be classified into acoprecipitation process, a citrate complex process, and an alkoxideprocess.

In the coprecipitation process, in at least any one of the steps ofpreparing an aqueous mixed salt solution (pre-crystallizationcomposition) containing salts of the above-mentioned elements (elementcomponents) in a predetermined stoichiometric ratio, coprecipitating theaqueous mixed salt solution by the addition of a neutralizing agent toobtain a coprecipitate (pre-crystallization composition), drying the theresulting coprecipitate, and heat-treating the dried product thereof(pre-crystallization composition), the pre-crystallization compositionbefore subjecting to a heat treatment is mixed with powders of at leastone of theta-alumina and alpha-alumina.

Examples of the salts of the elements include inorganic salts such assulfates, nitrates, chlorides, and phosphates; and organic salts such asacetates and oxalates. The aqueous mixed salt solution can be prepared,for example, by adding the salts of the elements to water in suchproportions as to establish a predetermined stoichiometric ratio andmixing them with stirring.

The neutralizing agent includes, for example, organic bases such asammonia, triethylamine, and pyridine; and inorganic bases such as sodiumhydroxide, potassium hydroxide, potassium carbonate, and ammoniumcarbonate. The neutralizing agent is added dropwise to the aqueous mixedsalt solution so that the solution after the addition of theneutralizing agent has a pH of about 6 to 10.

The resulting coprecipitate is, where necessary, washed with water, isdried typically by vacuum drying or forced-air drying to obtain a driedproduct.

Alternatively, an aqueous mixed solution of elements excluding a noblemetal is coprecipitated to obtain a coprecipitate and a dried productobtained by drying the coprecipitate is mixed with a solutionorganometal salts of the noble metal to obtain a homogeneous mixedslurry, and then the homogeneous mixed slurry is dried to obtain a driedproduct (pre-crystallization composition).

In the coprecipitation process, the powder of at least one oftheta-alumina and alpha-alumina may be added, for example, to theprepared aqueous mixed salt solution (pre-crystallization composition),the resulting coprecipitate (pre-crystallization composition), or adried product thereof (pre-crystallization composition), wherenecessary, in the form of a slurry or solution to obtain a mixture, andthe mixture is heat-treated, for example, at about 500° C. to 1000° C.,and preferably at about 600° C. to 950° C., thereby to obtain a powderyexhaust gas purifying catalyst comprising at least one of theta-aluminaand alpha-alumina supporting a perovskite-type composite oxide.

In the citrate complex process, for example, in at least any one of thesteps of preparing an aqueous citrate mixed salt solution(pre-crystallization composition) containing citric acid and the saltsof the respective elements (element component) in such proportions as toestablish a predetermined stoichiometric ratio of the salts of therespective elements, evaporating the aqueous citrate mixed salt solutionto dryness to form a dried product (pre-crystallization composition) ofa citrate complex of the respective elements, and heat-treating theresulting dried product, the pre-crystallization composition beforesubjecting to a heat treatment is mixed with powders of at least one oftheta-alumina and alpha-alumina.

The same as listed above can be used as the salts of the elementsherein. The aqueous citrate mixed salt solution can be prepared byinitially preparing an aqueous mixed salt solution by the aboveprocedure and adding an aqueous solution of citric acid to the aqueousmixed salt solution.

The evaporation to dryness is carried out at such a temperature at whichthe formed citrate complex is not decomposed, for example, at roomtemperature to about 150° C., thereby to remove the fluid immediately.The citrate complex of the elements is thus obtained.

Alternatively, an aqueous citrate mixed salt solution containing therespective elements excluding a noble metal is prepared and dried toform a citrate complex, and a heat-treated product obtained by a heattreatment of the citrate complex is mixed with a solution of organometalsalts of a noble metal to prepare a homogeneous mixed slurry, and thenthe homogeneous mixed slurry is dried to obtain a dried product(pre-crystallization composition).

In the citrate complex process, the powder of at least one oftheta-alumina and alpha-alumina may be added, for example, to at leastone of the prepared aqueous citrate mixed salt solution(pre-crystallization composition) and a dried product thereof(pre-crystallization composition), where necessary, in the form of aslurry or solution to obtain a mixture, and the mixture is heated, forexample, at 250° C. or higher in vacuum or in an inert atmosphere, andthen heat-treated, for example, at about 500° C. to 1000° C., andpreferably at about 600° C. to 950° C., thereby to obtain a powderyexhaust gas purifying catalyst comprising at least one of theta-aluminaand alpha-alumina supporting a perovskite-type composite oxide.

In the alkoxide process, for example, in at least any one of the stepsof preparing a mixed alkoxide solution (pre-crystallization composition)containing alkoxides of the respective elements excluding the noblemetal in the stoichiometric ratio, precipitating the mixed alkoxidesolution on hydrolysis by adding an aqueous solution containing salts ofthe noble metal thereto to obtain a precipitate (pre-crystallizationcomposition), drying the precipitate and heat-treating the resultingdried product (pre-crystallization composition), the pre-crystallizationcomposition before subjecting to a heat treatment is mixed with powdersof at least one of theta-alumina and alpha-alumina.

Examples of the alkoxides of the respective elements include alcholateseach comprising the element and an alkoxy such as methoxy, ethoxy,propoxy, isopropoxy, or butoxy; and alkoxyalcholates of the respectiveelements represented by the following general formula (8):E[OCH(R¹)—(CH₂)_(i)—OR² ]j  (8)wherein E represents the element; R¹ represents a hydrogen atom or analkyl group having 1 to 4 carbon atoms; R² represents an alkyl grouphaving 1 to 4 carbon atoms; i represents an integer of 1 to 3; and jrepresents an integer of 2 to 4.

More specific examples of the alkoxyalcholates include methoxyethylate,methoxypropylate, methoxybutylate, ethoxyethylate, ethoxypropylate,propoxyethylate, and butoxyethylate.

The mixed alkoxide solution can be prepared, for example, by adding thealkoxides of the respective elements to an organic solvent so as toestablish the stoichiometric ratio and mixing them with stirring. Theorganic solvent is not specifically limited, as long as it can dissolvethe alkoxides of the respective elements. Examples of such organicsolvents include aromatic hydrocarbons, aliphatic hydrocarbons,alcohols, ketones, and esters. Among these organic solvents, aromatichydrocarbons such as benzene, toluene, and xylene are preferred.

Subsequently, the mixed alkoxide solution is precipitated by adding anaqueous solution containing salts of the noble metals in a predeterminedstoichiometric ratio. Examples of the aqueous solution containing saltsof the noble metals include aqueous nitrate solution, aqueous chloridesolution, aqueous hexaammine chloride solution, aqueous dinitrodiamminenitrate solution, hexachloro acid hydrate, and potassium cyanide salt.

The resulting precipitate (pre-crystallization composition) is thendried typically by vacuum drying or forced-air drying to obtain a driedproduct (pre-crystallization composition).

In the alkoxide process, the powder of at least one of theta-alumina andalpha-alumina may be added, for example, to the prepared mixed alkoxidesolution (pre-crystallization composition), the resulting coprecipitate(pre-crystallization composition), or a dried product thereof(pre-crystallization composition), where necessary, in the form of aslurry or solution to obtain a mixture, and the mixture is heat-treated,for example, at about 500° C. to 1000° C., and preferably at about 500°C. to 850° C., thereby to obtain an exhaust gas purifying catalystcomprising at least one of theta-alumina and alpha-alumina supporting aperovskite-type composite oxide.

In the alkoxide process, a solution containing organometal salts of thenoble metals is added to the mixed alkoxide solution to obtain ahomogenous mixed solution (pre-crystallization composition).

Examples of the organometal salts of the noble metals include metalchelate complexes of the noble metals derived from, for example,β-diketone compounds or β-ketoester compounds represented by thefollowing general formula (6) and/or β-dicarboxylic ester compoundsrepresented by the following general formula (7):R³COCHR⁵COR⁴  (6)wherein R³ represents an alkyl group having 1 to 6 carbon atoms, afluoroalkyl group having 1 to 6 carbon atoms or an aryl group; R⁴represents an alkyl group having 1 to 6 carbon atoms, a fluoroalkylgroup having 1 to 6 carbon atoms, an aryl group or an alkyloxy grouphaving 1 to 4 carbon atoms; and R⁵ represents a hydrogen atom or analkyl group having 1 to 4 carbon atoms,R⁷CH(COOR⁶)₂  (7)wherein R⁶ represents an alkyl group having 1 to 6 carbon atoms; and R⁷represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms.

In the above-mentioned general formulas (6) and (7), examples of thealkyl groups each having 1 to 6 carbon atoms as R³, R⁴, and R⁶ includemethyl, ethyl, propyl, isopropyl, n-butyl, s-butyl, t-butyl, t-amyl, andt-hexyl. Examples of the alkyl groups each having 1 to 4 carbon atoms asR⁵ and R⁷ include methyl, ethyl, propyl, isopropyl, n-butyl, s-butyl,and t-butyl. The fluoroalkyl groups each having 1 to 6 carbon atoms asR³ and R⁴ include, for example, trifluoromethyl. The aryl groups as R³and R⁴ include, for example, phenyl. The alkyloxy group having 1 to 4carbon atoms as R⁴ includes, for example, methoxy, ethoxy, propoxy,isopropoxy, n-butoxy, s-butoxy, and t-butoxy.

More specific examples of the β-diketone compounds include2,4-pentanedione, 2,4-hexanedione, 2,2-dimethyl-3,5-hexanedione,1-phenyl-1,3-butanedione, 1-trifluoromethyl-1,3-butanedione,hexafluoroacetylacetone, 1,3-diphenyl-1,3-propanedione, anddipivaloylmethane. Examples of the β-ketoester compounds include methylacetoacetate, ethyl acetoacetate, and t-butyl acetoacetate. Examples ofthe β-dicarboxylic ester compounds include dimethyl malonate and diethylmalonate.

The solution containing the organometal salts of the noble metals can beprepared, for example, by adding the organometal salts of the noblemetals to an organic solvent so as to establish the stoichiometric ratioand mixing them with stirring. The same as listed above can be used asthe organic solvent herein.

In at least any one of the steps of mixing thus-prepared solutioncontaining the organometal salts of the noble metals with the mixedalkoxide solution to prepare the homogenous mixed solution(pre-crystallization composition), precipitating the homogenous mixedsolution by adding water thereto to obtain a precipitate(pre-crystallization composition), drying the precipitate andheat-treating the dried product (pre-crystallization composition), thepowder of at least one of theta-alumina and alpha-alumina may be added,where necessary, in the form of a solution to obtain a mixture, and themixture is heat-treated at about 400° C. to 1000° C., and preferably atabout 500° C. to 850° C., thereby to obtain an exhaust gas purifyingcatalyst comprising at least one of theta-alumina and alpha-aluminasupporting a perovskite-type composite oxide.

In the alkoxide process, preparation of a homegeneous mixed solutioncontaining organometal salts of the noble metal is prepared allows atleast one of theta-alumina and alpha-alumina to support theperovskite-type composite oxide in the state of being sufficientlydispersed, and can improve catalytic activity. Namely, mixing of thehomogenous mixed solution with a powder of at least one of theta-aluminaand alpha-alumina allows at least one of theta-alumina and alpha-aluminato support the perovskite-type composite oxide in the state of beingmore sufficiently dispersed as compared with the case of mixing themixed alkoxide solution with a powder of at least one of theta-aluminaand alpha-alumina, and can improve catalytic activity furthermore.

If the homogeneous mixed solution is prepared in such a manner, bubblingover in a heat treatment can be prevented as compared with the case ofpreparing the element component constituting the perovskite-typecomposite oxide in the form of an aqueous mixed salt solution, and thusthe catalyst can be industrially efficiently produced. This method doesnot yield harmful by-products and is excellent in safety or hygiene.Furthermore, the method can securely form a crystal structure of theperovskite-type composite oxide while suppressing a heat treatmenttemperature, and can effectively prevent a decrease in specific surfacearea.

According to the method for producing an exhaust gas purifying catalyst,since the perovskite-type composite oxide is supported by the powder ofat least one of theta-alumina and alpha-alumina, the perovskite-typecomposite oxide is stable and has a less reduced specific surface area,and also can keep its thermostability at a sufficient level even inendurance in high temperature oxidative-reducing atmospheres, thereby toeffectively avoid the catalytic performance from decreasing. This methodcan industrially efficiently produce the exhaust gas purifying catalyst.

The exhaust gas purifying catalyst thus obtained may further be mixedwith at least one thermostable oxide selected from the group consistingof zirconia composite oxides, ceria composite oxides, theta-alumina,alpha-alumina, gamma-alumina, SrZrO₃ and LaAlO₃. By mixing with any ofthese thermostable oxides, the perovskite-type composite oxide can havefurther improved thermostability. This easily enables the exhaust gaspurifying catalyst of the present invention to be used in a very severeatmosphere of high temperature such as in manifold converters.

The zirconia composite oxides are preferably represented by thefollowing general formula (9):Zr_(1−(a+b))Ce_(a)R_(b)O_(2−c)  (9)wherein R represents at least one of alkaline earth metals andrare-earth elements excluding Ce; a represents an atomic ratio of Cesatisfying the following relation: 0.1≦a≦0.65; b represents an atomicratio of R satisfying the following relation: 0≦b≦0.55; [1−(a+b)]represents an atomic ratio of Zr satisfying the following relation:0.35≦[1−(a+b)]≦0.9; and c represents an oxygen defect.

Examples of the alkaline earth metals represented by R include Be, Mg,Ca, Sr, Ba, and Ra, of which Mg, Ca, Sr, and Ba are preferred. Therare-earth elements represented by R are rare-earth elements excludingCe, and examples thereof include Sc, Y, La, Pr, Nd, Pm, Sm, Eu, Gd, Tb,Dy, Ho, Er, Tm, Yb, and Lu. Among them, Sc, Y, La, Pr, and Nd arepreferred. These alkaline earth metals and rare-earth elements can beused alone or in combination.

The atomic ratio of Ce represented by a ranges from 0.1 to 0.65. If theatomic ratio is less than 0.1, the crystal phase may become unstable todecompose in oxidative-reducing atmospheres at high temperatures,thereby to decrease the catalytic performance. If it exceeds 0.65, thecatalyst may have a decreased specific surface area, thereby to fail toexhibit satisfactory catalytic performance. The atomic ratio of Rrepresented by b ranges from 0 to 0.55. Namely, R is not an essentialcomponent but is an optional component to be contained optionally. Theatomic ratio thereof is, if contained, 0.55 or less. An atomic ratio ofR exceeding 0.55 may invite phase separation or formation of othercomposite oxide phases.

The atomic ratio of Zr represented by [1−(a+b)] ranges from 0.35 to 0.9.The atomic ratio of Zr is preferably ranges from 0.5 to 0.9 and morepreferably ranges from 0.6 to 0.9.

The zirconia composite oxide represented by the general formula (9)preferably has an atomic ratio of Ce of 0.5 or less. When the exhaustgas purifying catalyst comprises the zirconia composite oxiderepresented by the general formula (9) in combination with the ceriacomposite oxide represented by the general formula (10) mentioned below,the atomic ratio of Zr in the zirconia composite oxide represented bythe general formula (9) is preferably greater than the atomic ratio ofZr in the ceria composite oxide represented by the general formula (10).

The amount c represents an oxygen defect which in turn means a ratio ofvacancies formed in a fluorite-like crystal lattice generally composedof oxides of Zr, Ce and R.

These zirconia composite oxides can be prepared according to any ofknown processes without being limited to a particular process.

The ceria composite oxides are preferably represented by the followinggeneral formula (10):Ce_(1−(d+e))Zr_(d)L_(e)O_(2−f)  (10)wherein L represents at least one of alkaline earth metals andrare-earth elements excluding Ce; d represents an atomic ratio of Zrsatisfying the following relation: 0.2≦d≦0.7; e represents an atomicratio of L satisfying the following relation: 0≦e≦0.2; [1−(d+e)]represents an atomic ratio of Ce satisfying the following relation:0.3≦[1−(d+e)]≦0.8; and f represents an oxygen defect.

The same as the alkaline earth metals and rare-earth elementsrepresented by R can be used as the alkaline earth metals and/orrare-earth elements represented by L. Preferred examples of the alkalineearth metals include Mg, Ca, Sr, and Ba, and preferred examples of therare-earth elements include Sc, Y, La, Pr, and Nd. These alkaline earthmetals and rare-earth elements can be used alone or in combination.

The atomic ratio of Zr represented by d ranges from 0.2 to 0.7. If theatomic ratio is less than 0.2, the resulting catalyst may have adecreased specific surface area, thereby to fail to exhibit sufficientcatalytic performance. If it exceeds 0.7, the catalyst may havedecreased oxygen occlusion capability to fail to exhibit sufficientcatalytic performance. The atomic ratio of L represented by e rangesfrom 0 to 0.2. Namely, L is not an essential component but an optionalcomponent to be contained optionally in an atomic ratio of, ifcontained, 0.2 or less. An atomic ratio of L exceeding 0.2 may invitephase separation or formation of other composite oxide phases.

The atomic ratio of Ce represented by [1−(d+e)] ranges from 0.3 to 0.8,and preferably ranges from 0.4 to 0.6.

The ceria composite oxides represented by the general formula (10) eachpreferably have an atomic ratio of Zr of 0.5 or less. When used incombination with the zirconia composite oxide represented by the generalformula (9) in the exhaust gas purifying catalyst, the atomic ratio ofCe in the ceria composite oxide represented by the general formula (10)is preferably greater than the atomic ratio of Ce in the zirconiacomposite oxide represented by the general formula (9).

The amount f represents an oxygen defect which in turn means a ratio ofvacancies formed in a fluorite-like crystal lattice generally composedof oxides of Ce, Zr and L.

These ceria composite oxides can be prepared by the same procedures asin the production of the zirconia composite oxides.

When the zirconia composite oxide or the ceria composite oxide actuallyused has an atomic ratio falling both within the atomic ratios of therespective elements of the zirconia composite oxides represented by thegeneral formula (9) and within the atomic ratios of the respectiveelements of the ceria composite oxides represented by the generalformula (10), it can be classified as any of these composite oxideswithout being limited to a particular category. The category, forexample, is appropriately set according to the formulation to beincorporated when a plurality of the zirconia composite oxides and/orthe ceria composite oxides are used. When the noble metals aresupported, for example, the ceria composite oxide can be distinguishedfrom the zirconia composite oxide by allowing the ceria composite oxideto support not Rh but Pt alone.

The same as listed above can be used as the theta-alumina herein.

Likewise, the same as listed above can be used as the alpha-aluminaherein.

The theta-alumina and/or alpha-alumina to be mixed in these supportingembodiments may comprise La and/or Ba, as is described above. Namely,one represented by the following general formula (5) is preferably used:(Al_(1-g)D_(g))₂O₃  (5)wherein D represents La and/or Ba; and g represents an atomic ratio of Dsatisfying the following relation: 0≦g≦0.5.

D represents La and/or Ba, and the atomic ratio of D represented by granges from 0 to 0.5. Namely, La and/or Ba is not an essential componentbut an optional component to be contained optionally in an atomic ratioof, if contained, 0.5 or less.

The gamma-alumina includes, but is not specifically limited to, knowngamma-alumina used as an exhaust gas purifying catalyst.

SrZrO₃ can be prepared, for example, by the procedure of the productionmethod of the zirconia composite oxides using a zirconium salt and astrontium salt, or an alkoxide of zirconium and an alkoxide ofstrontium.

LaAlO₃ can be prepared, for example, by the procedure of the productionmethod of the zirconia composite oxides using a lanthanum salt and analuminum salt, or an alkoxide of lanthanum and an alkoxide of aluminum.

The amount of the thermostable oxides is not specifically limited andis, for example, such that the total amount of the thermostable oxidesfalls within a range of 0.5 to 30 parts by weight, and preferably 0.5 to10 parts by weight, to 1 part by weight of at least one of theta-aluminaand alpha-alumina which supports the perovskite-type composite oxide. Ifthe amount of the thermostable oxides is less than the above-specifiedrange, the catalyst may not have sufficiently improved thermostability.If it is more than the above-specified range, the catalyst may comprisean excess amount of thermostable oxides, which may invite disadvantagesin cost and production.

The mixing procedure of the thermostable oxides is not specificallylimited, as long as it can physically mix the thermostable oxides withat least one of theta-alumina and alpha-alumina supporting theperovskite-type composite oxide. For example, a powder of at least oneof theta-alumina and alpha-alumina supporting the perovskite-typecomposite oxide may be mixed with a powder of the thermostable oxides bydry-mixing or wet-mixing.

The thermostable oxide preferably comprises a thermostable oxidesupporting a noble metal. By incorporating the thermostable oxidesupporting a noble metal, the resulting catalyst can have a furtherincreased catalytic activity and further improved catalytic performance,in addition to the action of the noble metal contained in theperovskite-type composite oxide containing a noble metal.

Examples of the noble metal herein include Pd, Rh, and Pt, of which Rhand Pt are preferred. These noble metals can be used alone or incombination.

The noble metal can be supported by the thermostable oxide according toa known procedure not specifically limited. It can be supported, forexample, by preparing a salt-containing solution comprising the noblemetal, impregnating the thermostable oxide with the salt-containingsolution and baking the resulting article.

The same as listed above can be used as the salt-containing solution.Practical examples thereof include aqueous nitrate solution,dinitrodiammine nitrate solution, and aqueous chloride solution. Morespecifically, examples of the palladium salt solution include aqueouspalladium nitrate solution, dinitrodiammine palladium nitrate solution,and palladium tetraammine nitrate solution. Examples of the rhodium saltsolution include rhodium nitrate solution and rhodium chloride solution.Examples of the platinum salt solution include dinitrodiammine platinumnitrate solution, chloroplatinic acid solution, and platinum tetraamminesolution.

After impregnating the thermostable oxide with the noble metal, theresulting article is dried, for example, at 50° C. to 200° C. for 1 to48 hours and is baked at 350° C. to 1000° C. for 1 to 12 hours.

Alternatively, the noble metal can be supported by the thermostableoxide, for example, in the following manner. When the thermostable oxideis the zirconia composite oxide or the ceria composite oxide, the noblemetal is coprecipitated with the respective components of the zirconiacomposite oxide or the ceria composite oxide by adding a solution of thenoble metal salt during coprecipitation or hydrolysis of the saltsolution or mixed alkoxide solution containing zirconium, cerium and thealkaline earth metal and/or the rare-earth element, and thecoprecipitate is then baked.

Another example of a method for allowing the thermostable oxide tosupport the noble metal is as follows. When the thermostable oxide isone of the theta-alumina, alpha-alumina, and gamma-alumina, the noblemetal is coprecipitated with the theta-alumina, alpha-alumina, orgamma-alumina by adding a solution of the noble metal salt duringprecipitation (deposition) of the theta-alumina, alpha-alumina, orgamma-alumina from an aqueous aluminum salt solution typically usingammonia in its production process, and the coprecipitate is baked.

When two or more different noble metals are supported, these noblemetals may be supported simultaneously in one step or sequentially inplural steps.

The amount of the noble metals is set according to the purpose and usethereof and is, for example, 0.01% to 3.0% by weight, and preferably0.05% to 1.0% by weight of the total amount of the thermostable oxides.

Examples of the thermostable oxide supporting a noble metal thusprepared include a zirconia composite oxide supporting a noble metal, aceria composite oxide supporting a noble metal, a theta-aluminasupporting a noble metal and a gamma-alumina supporting a noble metal.

The zirconia composite oxide supporting a noble metal is preferably azirconia composite oxide supporting Pt and/or Rh. In this case, theamount of Pt and/or Rh is 0.01% to 2.0% by weight, and preferably 0.05%to 1.0% by weight of the amount of the zirconia composite oxide.

The ceria composite oxide supporting a noble metal is preferably a ceriacomposite oxide supporting Pt. In this case, the amount of Pt is 0.01%to 2.0% by weight, and preferably 0.05% to 1.0% by weight of the amountof the ceria composite oxide.

The theta-alumina supporting a noble metal is preferably a theta-aluminasupporting Pt and/or Rh. In this case, the amount of Pt and/or Rh is0.01% to 2.0% by weight, and preferably 0.05% to 1.0% by weight of theamount of the theta-alumina.

The gamma-alumina supporting a noble metal is preferably a gamma-aluminasupporting Pt and/or Rh. In this case, the amount of Pt and/or Rh is0.01% to 2.0% by weight, and preferably 0.05% to 1.0% by weight of theamount of the gamma-alumina.

Of these thermostable oxides each supporting a noble metal, the ceriacomposite oxide supporting a noble metal is preferred. The use of theceria composite oxide supporting a noble metal can improve the oxygenstorage performance.

The entire thermostable oxide may support the noble metal.Alternatively, the thermostable oxide may comprise both a thermostableoxide supporting the noble metal and a thermostable oxide not supportingthe noble metal.

The exhaust gas purifying catalyst obtained by the method of the presentinvention can constitute, for example, a coating layer on a catalystcarrier. The catalyst carrier can be any of known catalyst carriers suchas honeycomb monolith carriers derived from cordierite, without beinglimited to a particular catalyst carrier.

The coating layer can be formed on the catalyst carrier, for example, inthe following manner. Initially, water is added to at least one oftheta-alumina and alpha-alumina supporting the perovskite-type compositeoxide as well as the thermostable oxide added according to necessity toobtain a slurry. The slurry is then applied to the catalyst carrier, isdried at 50° C. to 200° C. for 1 to 48 hours and is baked at 350° C. to1000° C. for 1 to 12 hours. Alternatively, the coating layer can beformed by adding water to each of the respective components to obtainslurries, mixing these slurries, applying the resulting slurry mixtureto the catalyst carrier, drying at 50° C. to 200° C. for 1 to 48 hoursand then baking at 350° C. to 1000° C. for 1 to 12 hours.

The exhaust gas purifying catalyst obtained by the method of the presentinvention can also be arranged as a multilayer coating layer on thecatalyst carrier. The multilayer coating layer comprises an outer layerconstituting its surface and an inner layer arranged inside the outerlayer.

The inner layer can be prepared by applying the slurry containing therespective components to the catalyst carrier, drying and baking theresulting article, as described above. The outer layer can be preparedby applying the slurry containing the respective components to the innerlayer formed on the catalyst carrier, drying and baking the resultingarticle, as described above.

When the exhaust gas purifying catalyst obtained by the method of thepresent invention comprises multiple layers, it is preferred that theinner layer comprises the theta-alumina and/or alpha-alumina supportingthe perovskite-type composite oxide.

By incorporating at least one of theta-alumina and alpha-aluminasupporting the perovskite-type composite oxide into the inner layer, thecatalyst can be prevented from poisoning and thermal degradation and canexhibit further improved catalytic performance.

When the exhaust gas purifying catalyst obtained by the method of thepresent invention comprises the multiple layers as above, at least oneof theta-alumina and alpha-alumina supporting the perovskite-typecomposite oxide can be used alone or in combination. Specifically, forexample, at least one of theta-alumina and alpha-alumina supporting theperovskite-type composite oxide can be contained in the inner layeralone or the outer layer alone. In addition, the same or different typesof plural theta-alumina and/or alpha-alumina supporting perovskite-typecomposite oxide may be contained in either one of the inner layer andouter layer or in both of the inner layer and outer layer.

When the exhaust gas purifying catalyst obtained by the method of thepresent invention comprises the multiple layers, at least one oftheta-alumina and alpha-alumina supporting the Pd containingperovskite-type composite oxide is preferably contained in the innerlayer. By incorporating at least one of theta-alumina and alpha-aluminasupporting the Pd containing perovskite-type composite oxide into theinner layer, the poisoning and thermal degradation of Pd contained inthe perovskite-type composite oxide can be prevented, thereby to improvethe durability.

When the exhaust gas purifying catalyst obtained by the method of thepresent invention comprises the multiple layers, at least one oftheta-alumina and alpha-alumina supporting the Rh containingperovskite-type composite oxide is preferably contained in the outerlayer. By incorporating at least one of theta-alumina and alpha-aluminasupporting the Rh containing perovskite-type composite oxide into theouter layer, alloying with Pd can be prevented typically in the casewhere the Pd containing perovskite-type composite oxide is contained inthe inner layer.

When the exhaust gas purifying catalyst obtained by the method of thepresent invention comprises the multiple layers, at least one oftheta-alumina and alpha-alumina supporting the Pt containingperovskite-type composite oxide is preferably contained in the innerlayer and/or the outer layer.

When the exhaust gas purifying catalyst obtained by the method of thepresent invention comprises the multiple layers, it is preferred thatthe noble metal contained in the outer layer (including the noble metalcontained in the perovskite-type composite oxide, and the noble metalsupported by the thermostable oxide) is Rh and/or Pt and that the noblemetal contained in the inner layer (including the noble metal containedin the perovskite-type composite oxide, and the noble metal supported bythe thermostable oxide) is at least Pd. This configuration can preventthe poisoning and thermal degradation of the catalyst by incorporatingPd into the inner layer and can further improve the catalyticperformance by the action of Rh and/or Pt contained in the outer layer.

When the exhaust gas purifying catalyst obtained by the method of thepresent invention comprises the multiple layers, it is preferred thatthe ceria composite oxide and/or theta-alumina each supporting a noblemetal is contained in the inner layer, and that at least two differentthermostable oxides selected from the zirconium composite oxidesupporting a noble metal, the ceria composite oxide supporting a noblemetal, the theta-alumina supporting a noble metal, and the gamma-aluminasupporting a noble metal are contained in the outer layer.

More specifically, it is preferred that the inner layer comprises thetheta-alumina and the ceria composite oxide supporting Pt and that theouter layer comprises at least one thermostable oxide selected from thegroup consisting of the zirconia composite oxide supporting Pt and Rh,the ceria composite oxide supporting Pt, and the theta-aluminasupporting Pt and Rh.

The exhaust gas purifying catalyst of the present invention may furthercomprise any of sulfates, carbonates, nitrates, and acetates of Ba, Ca,Sr, Mg, and La. Any of these sulfates, carbonates, nitrates, andacetates is preferably contained in a layer containing Pd, when thecatalyst comprises the multiple layers. By incorporating any of thesulfates, carbonates, nitrates, and acetates, the poisoning of Pdtypically by the action of hydrocarbons (HC) can be prevented, therebyto avoid decrease in catalytic activity. Of these salts, BaSO₄ ispreferably used.

The amount of any of these sulfates, carbonates, nitrates, and acetatesmay be appropriately set depending on the purpose and the use thereof.The sulfate, carbonate, nitrate, and/or acetate can be incorporated intothe inner layer and/or the outer layer, for example, by adding thesulfate, carbonate, nitrate, and/or acetate into the slurry for formingthe inner layer and/or the outer layer.

The inner layer may comprise multiple layers, according to the purposeand use thereof. The same procedure as above can be applied to form theinner layer as multiple layers.

The exhaust gas purifying catalyst obtained by the method of the presentinvention thus obtained can allow a noble metal to be stably containedin a perovskite-type composite oxide and, in addition, remarkablyincrease the thermostability of the perovskite-type composite oxide bythe action of at least one of theta-alumina and alpha-alumina becausethe perovskite-type composite oxide is supported by at least one oftheta-alumina and alpha-alumina.

In each perovskite-type composite oxide, the noble metal is finely andhighly dispersed, thereby to maintain its high catalytic activity evenin long-term use in an atmosphere of high temperature. This is becauseof the self-regenerative function in which the noble metal repetitivelyundergoes solid-solution under an oxidative atmosphere and depositionunder a reducing atmosphere with respect to the perovskite structure.This self-regenerative function also enables the resulting catalyst toachieve satisfactory catalytic activity even if the amount of the noblemetal is significantly reduced.

The perovskite-type composite oxide exhibits increased thermostabilityby the action of at least one of theta-alumina and alpha-alumina. Thisprevents the perovskite-type composite oxide from grain growth and adecreased specific surface area in an atmosphere of high temperature of,for example, 900° C. to 1000° C., or further exceeding 1050° C.

Thus, the exhaust gas purifying catalyst obtained by the method of thepresent invention can maintain the catalytic activity of the noble metalat a high level over a long time and achieve satisfactory exhaust gaspurifying performance, even in an atmosphere of high temperatureexceeding 900° C. to 1000° C. It can be advantageously used as anexhaust gas purifying catalyst for automobiles.

EXAMPLES

The present invention will be illustrated in further detail withreference to several examples and comparative examples below, which arenever intended to limit the scope of the invention.

(1) Production of Zirconia Composite Oxide

Production Example A1

Zirconium oxychloride 16.9 g (0.050 mol) Cerium nitrate 17.4 g (0.040mol) Lanthanum nitrate  2.2 g (0.005 mol) Neodymium nitrate  2.2 g(0.005 mol)

The above listed components were dissolved in 100 mL of deionized waterto obtain an aqueous mixed salt solution. Separately, 25.0 g of sodiumcarbonate was dissolved in 200 mL of deionized water to obtain analkaline aqueous solution, and the aqueous mixed salt solution wasgradually added dropwise thereto to form a coprecipitate. After beingfully washed with water and filtrated, the coprecipitate was fully driedat 80° C. in vacuum. The coprecipitate was then heat treated (calcined)at 800° C. for one hour to obtain a powdery zirconia composite oxide(Production Example A1) comprising aZr_(0.50)Ce_(0.40)La_(0.05)Nd_(0.05) oxide, in which cerium andlanthanum constitute a solid solution.

The powdery zirconia composite oxide was impregnated with adinitrodiammine platinum nitrate solution, dried at 100° C., furtherimpregnated with a rhodium nitrate solution, dried at 100° C. and bakedat 500° C. to obtain a powdery Pt—Rh supporting zirconia composite oxide(Production Example A1-1) supporting 0.27% by weight of Pt and 1.33% byweight of Rh.

Production Example A2

Zirconium oxychloride 25.6 g (0.076 mol)  Cerium nitrate 7.8 g (0.018mol) Lanthanum nitrate 1.7 g (0.002 mol) Neodymium nitrate 1.8 g (0.004mol)

The above listed components were dissolved in 100 mL of deionized waterto obtain an aqueous mixed salt solution. Separately, 25.0 g of sodiumcarbonate was dissolved in 200 mL of deionized water to obtain analkaline aqueous solution, and the aqueous mixed salt solution wasgradually added dropwise thereto to form a coprecipitate. After beingfully washed with water and filtrated, the coprecipitate was fully driedat 80° C. in vacuum. The coprecipitate was then heat treated (calcined)at 800° C. for one hour to obtain a powdery zirconia composite oxide(Production Example A2) comprising aZr_(0.76)Ce_(0.18)La_(0.02)Nd_(0.04) oxide, in which cerium andlanthanum constitute a solid solution.

The powdery zirconia composite oxide was impregnated with adinitrodiammine platinum nitrate solution, dried at 100° C., furtherimpregnated with a rhodium nitrate solution, dried at 100° C. and bakedat 500° C. to obtain a powdery Pt—Rh supporting zirconia composite oxide(Production Example A2-1) supporting 1.00% by weight of Pt and 1.00% byweight of Rh, or a powdery Pt—Rh supporting zirconia composite oxide(Production Example A2-2) supporting 0.27% by weight of Pt and 1.33% byweight of Rh.

Production Example A3

Zirconium oxychloride 16.9 g (0.050 mol) Cerium nitrate 17.4 g (0.040mol) Lanthanum nitrate  2.2 g (0.005 mol) Yttrium nitrate  1.9 g (0.005mol)

The above listed components were dissolved in 100 mL of deionized waterto obtain an aqueous mixed salt solution. Separately, 25.0 g of sodiumcarbonate was dissolved in 200 mL of deionized water to obtain analkaline aqueous solution, and the aqueous mixed salt solution wasgradually added dropwise thereto to form a coprecipitate. After beingfully washed with water and filtrated, the coprecipitate was fully driedat 80° C. in vacuum. The dried coprecipitate heat treated (calcined) at800° C. for one hour to obtain a powdery zirconia composite oxide(Production Example A3) comprising a Zr_(0.50)Ce_(0.40)La_(0.05)Y_(0.05)oxide, in which cerium and lanthanum constitute a solid solution.

Production Example A4

Zirconium oxychloride 23.6 g (0.070 mol) Cerium nitrate 10.8 g (0.025mol) Lanthanum nitrate  1.7 g (0.002 mol) Neodymium nitrate  1.3 g(0.003 mol)

The above listed components were dissolved in 100 mL of deionized waterto obtain an aqueous mixed salt solution. Separately, 25.0 g of sodiumcarbonate was dissolved in 200 mL of deionized water to obtain analkaline aqueous solution, and the aqueous mixed salt solution wasgradually added dropwise thereto to form a coprecipitate. After beingfully washed with water and filtrated, the coprecipitate was fully driedat 80° C. in vacuum. The dried coprecipitate heat treated (calcined) at800° C. for one hour to obtain a powdery zirconia composite oxide(Production Example A4) comprising aZr_(0.70)Ce_(0.25)La_(0.02)Nd_(0.03) oxide in which cerium and lanthanumconstitute a solid solution.

The powdery zirconia composite oxide was impregnated with adinitrodiammine platinum nitrate solution, dried at 100° C., furtherimpregnated with a rhodium nitrate solution, dried at 100° C. and bakedat 500° C. to obtain a powdery Pt—Rh supporting zirconia composite oxide(Production Example A4-1) supporting 0.75% by weight of Pt and 1.25% byweight of Rh.

Production Example A5

Zirconium oxychloride 23.6 g (0.070 mol) Cerium nitrate 10.8 g (0.025mol) Lanthanum nitrate  1.7 g (0.002 mol) Yttrium nitrate  1.1 g (0.003mol)

The above listed components were dissolved in 100 mL of deionized waterto obtain an aqueous mixed salt solution. Separately, 25.0 g of sodiumcarbonate was dissolved in 200 mL of deionized water to obtain analkaline aqueous solution, and the aqueous mixed salt solution wasgradually added dropwise thereto to form a coprecipitate. After beingfully washed with water and filtrated, the coprecipitate was fully driedat 80° C. in vacuum. The dried coprecipitate heat treated (calcined) at800° C. for one hour to obtain a powdery zirconia composite oxide(Production Example A5) comprising a Zr_(0.70)Ce_(0.25)La_(0.02)Y_(0.03)oxide in which cerium and lanthanum constitute a solid solution.

Production Example A6

Zirconium ethoxyethylate 31.4 g (0.070 mol) Cerium ethoxyethylate 10.2 g(0.025 mol) Praseodymium ethoxyethylate  0.8 g (0.002 mol) Neodymiumethoxyethylate  1.2 g (0.003 mol)

The above listed components were dissolved in 200 mL of toluene withstirring to obtain a mixed alkoxide solution. The alkoxides werehydrolyzed by adding the mixed alkoxide solution dropwise to 600 mL ofdeionized water over about ten minutes. The toluene and deionized waterwere distilled off from the hydrolyzed solution to dryness to obtain adried product. After being subjected to forced air drying at 60° C. fortwenty four hours, the dried product heat treated (baked) in an electricfurnace at 800° C. for one hour to obtain a powdery zirconia compositeoxide (Production Example A6) comprising aZr_(0.70)Ce_(0.25)Pr_(0.02)Nd_(0.03) oxide.

(2) Production of Ceria Composite Oxide

Production Example B1

Cerium methoxypropylate 24.4 g (0.060 mol) Zirconium methoxypropylate13.4 g (0.030 mol) Yttrium methoxypropylate  3.6 g (0.010 mol)

The above listed components were dissolved in 200 mL of toluene withstirring to obtain a mixed alkoxide solution. The alkoxides werehydrolyzed by adding 80 mL of deionized water dropwise to the solution.The toluene and deionized water were distilled off from the hydrolyzedsolution to dryness to obtain a dried product. After being subjected toforced air drying at 60° C. for twenty four hours, the dried product wasbaked in an electric furnace at 450° C. for three hours to obtain apowdery ceria composite oxide (Production Example B1) comprising aCe_(0.60)Zr_(0.30)Y_(0.10) oxide.

The powdery ceria composite oxide was impregnated with a dinitrodiammineplatinum nitrate solution, dried at 100° C. and baked at 500° C. toobtain a powdery Pt supporting ceria composite oxide (Production ExampleB1-1) supporting 1.00% by weight of Pt; a powdery Pt supporting ceriacomposite oxide (Production Example B1-2) supporting 0.33% by weight ofPt; a powdery Pt supporting ceria composite oxide (Production ExampleB1-3) supporting 0.67% by weight of Pt; a powdery Pt supporting ceriacomposite oxide (Production Example B1-4) supporting 1.38% by weight ofPt; or a powdery Pt supporting ceria composite oxide (Production ExampleB1-5) supporting 1.50% by weight of Pt.

Production Example B2

Cerium methoxypropylate 12.2 g (0.030 mol) Zirconium methoxypropylate31.5 g (0.070 mol)

The above listed components were dissolved in 200 mL of toluene withstirring to obtain a mixed alkoxide solution. The alkoxides werehydrolyzed by adding 80 mL of deionized water dropwise to the solution.The toluene and deionized water were distilled off from the hydrolyzedsolution to dryness to obtain a dried product. After being subjected toforced air drying at 60° C. for twenty four hours, the dried product wasbaked in an electric furnace at 300° C. for three hours to obtain apowdery Ce_(0.30)Zr_(0.70)O₂ ceria composite oxide (Production ExampleB2).

The powdery ceria composite oxide was impregnated with a dinitrodiammineplatinum nitrate solution, dried at 100° C., further impregnated with arhodium nitrate solution, dried at 100° C. and baked at 500° C. toobtain a powdery Pt—Rh supporting ceria composite oxide (ProductionExample B2-1) supporting 2.00% by weight of Pt and 1.00% by weight ofRh.

(3) Production of Theta-Alumina

Production Example C1

Aluminum methoxyethylate 60.6 g (0.240 mol)  Lanthanum methoxyethylate0.55 g (0.0015 mol)

The above listed components were charged in a 500 mL round bottomedflask, dissolved in 300 mL of toluene with stirring to obtain ahomogeneous AlLa mixed alkoxide solution. Next, 200 mL of deionizedwater was added dropwise to the mixture over about fifteen minutes.Then, a gray viscous precipitate was formed upon hydrolysis.

After stirring at room temperature for two hours, the toluene and waterwere distilled off under reduced pressure to obtain a mixture of AlLacomposite oxides. Next, the mixture was placed on a petri dish,subjected to forced air drying at 60° C. for twenty four hours and heattreated in an electric furnace at 1000° C. in the air for four hours toobtain a powdery lanthanum containing theta-alumina (Production ExampleC1) containing 2.0% by weight of lanthanum in terms of La₂O₃.

Production Example C2

Aluminum methoxyethylate 59.4 g (0.236 mol) Lanthanum methoxyethylate 1.1 g (0.003 mol)

The above listed components were charged in a 500 mL round bottomedflask, dissolved in 300 mL of toluene with stirring to obtain ahomogeneous AlLa mixed alkoxide solution. Next, 200 mL of deionizedwater was added dropwise to the mixture over about fifteen minutes.Then, a gray viscous precipitate was formed upon hydrolysis.

After stirring at room temperature for two hours, the toluene and waterwere distilled off under reduced pressure to obtain a mixture of AlLacomposite oxides. Next, the mixture was placed on a petri dish,subjected to forced air drying at 60° C. for twenty four hours and heattreated in an electric furnace at 1000° C. in the air for four hours toobtain a powdery lanthanum containing theta-alumina (Production ExampleC2) containing 4.0% by weight of lanthanum in terms of La₂O₃.

Production Example C3

Aluminum methoxyethylate 44.6 g (0.177 mol) Lanthanum methoxyethylate 2.2 g (0.006 mol)

The above listed components were charged in a 500 mL round bottomedflask, dissolved in 300 mL of toluene with stirring to obtain ahomogeneous AlLa mixed alkoxide solution. Next, 200 mL of deionizedwater was added dropwise to the mixture over about fifteen minutes.Then, a gray viscous precipitate was formed upon hydrolysis.

After stirring at room temperature for two hours, the toluene and waterwere distilled off under reduced pressure to obtain a mixture of AlLacomposite oxides. Next, the mixture was placed on a petri dish,subjected to forced air drying at 60° C. for twenty four hours and heattreated in an electric furnace at 1000° C. in the air for four hours toobtain a powdery lanthanum containing theta-alumina (Production ExampleC3) containing 10.0% by weight of lanthanum in terms of La₂O₃.

Production Example C4

Aluminum methoxyethylate 59.4 g (0.236 mol) Barium methoxyethylate 0.95g (0.0033 mol)

The above listed components were charged in a 500 mL round bottomedflask, dissolved in 300 mL of toluene with stirring to obtain ahomogeneous AlBa mixed alkoxide solution. Next, 200 mL of deionizedwater was added dropwise to the mixture over about fifteen minutes.Then, a gray viscous precipitate was formed upon hydrolysis.

After stirring at room temperature for two hours, the toluene and waterwere distilled off under reduced pressure to obtain a mixture of AlBacomposite oxides. Next, the mixture was placed on a petri dish,subjected to forced air drying at 60° C. for twenty four hours and heattreated in an electric furnace at 1000° C. in the air for four hours toobtain a powdery barium containing theta-alumina (Production Example C4)containing 4.0% by weight of barium in terms of BaO.

Production Example C5

A powdery theta-alumina (having a specific surface area of 98.4 m²/g,the same is true hereafter) was impregnated with dinitrodiammineplatinum nitrate solution, dried at 100° C. and baked at 500° C. toobtain a Pt supporting theta-alumina (Production Example C5) supporting0.31% by weight of Pt.

Production Example C6

The powdery theta-alumina was impregnated with a dinitrodiammineplatinum nitrate solution, dried at 100° C., further impregnated with arhodium nitrate solution, dried at 100° C. and baked at 500° C. toobtain a powdery Pt—Rh supporting theta-alumina (Production ExampleC6-1) supporting 0.57% by weight of Pt and 0.14% by weight of Rh; apowdery Pt—Rh supporting theta-alumina (Production Example C6-2)supporting 0.43% by weight of Pt and 0.21% by weight of Rh; or a powderyPt—Rh supporting theta-alumina (Production Example C6-3) supporting1.50% by weight of Pt and 0.67% by weight of Rh.

Production Example C7

The powdery theta-alumina was impregnated with a palladium nitratesolution, dried at 100° C. and baked at 500° C. to obtain a powdery Pdsupporting theta-alumina (Production Example C7) supporting 1.10% byweight of Pd.

(4) Production of Gamma-Alumina

Production Example D1

A powdery gamma-alumina (having a specific surface area of 200 m²/g, thesame is true hereinafter) was impregnated with a dinitrodiammineplatinum nitrate solution, dried at 100° C., further impregnated with arhodium nitrate solution, dried at 100° C. and baked at 500° C. toobtain a powdery Pt—Rh supporting gamma-alumina (Production Example D1)supporting 1.00% by weight of Pt and 0.57% by weight of Rh.

Example QA-1

Lanthanum nitrate 43.3 g (0.100 mol) Iron nitrate 38.4 g (0.095 mol)

Aqueous palladium nitrate solution (Pd content of 4.399% by mass) 12.1 g(corresponding to 0.53 g (0.005 mol) of Pd)

The above listed components were dissolved in 200 mL of deionized waterto obtain an aqueous mixed salt solution. Next, 73.4 g of the powderytheta-alumina was mixed with the aqueous mixed salt solution withstirring, and an aqueous ammonium carbonate solution was added dropwisethereto until the aqueous mixed salt solution had a pH of 10, to form acoprecipitate. After being stirred for one hour, the coprecipitate wasfiltrated, was fully washed with water, subjected to forced air dryingat 120° C. for twelve hours, baked at 700° C. in the air for three hoursto obtain a powdery exhaust gas purifying catalyst comprising thetheta-alumina supporting a La_(1.00)Fe_(0.95)Pd_(0.05)O₃ perovskite-typecomposite oxide.

The resulting powder was prepared so as to have a weight ratio of theperovskite-type composite oxide to the theta-alumina of 1:3.

Example QA-2

Lanthanum methoxypropylate 40.6 g (0.100 mol) Iron methoxypropylate 30.7g (0.095 mol)

The above listed components were charged in a 1000 mL round bottomedflask, dissolved in 200 mL of toluene with stirring to obtain a mixedalkoxide solution. Separately, 1.52 g (0.005 mol) of palladiumacetylacetonate was dissolved in 20 mL of toluene, the resultingsolution was added to the mixed alkoxide solution in the round bottomedflask to obtain a homogeneous mixed solution containing LaFePd.

Next, 98.0 g of the powdery lanthanum containing theta-alumina(containing 4.0% by weight of La₂O₃) (Production Example C2) was mixedwith the homogeneous mixed solution with stirring, and 200 mL ofdeionized water was added dropwise thereto over about fifteen minutes.As a result, a brown viscous precipitate was formed upon hydrolysis.

After stirring at room temperature for two hours, the toluene and waterwere distilled off under reduced pressure to obtain a mixture of apre-crystallization composition of a LaFePd containing perovskite-typecomposite oxide homogeneously dispersed in the lanthanum containingtheta-alumina. Next, the mixture was placed on a petri dish, subjectedto forced air drying at 60° C. for twenty four hours and heat treated inan electric furnace at 800° C. in the air for one hour to obtain apowdery exhaust gas purifying catalyst comprising the lanthanumcontaining theta-alumina supporting a La_(1.00)Fe_(0.95)Pd_(0.05)O₃perovskite-type composite oxide.

The resulting powder was prepared so as to have a weight ratio of theperovskite-type composite oxide to the lanthanum containingtheta-alumina of 1:4.

Example QA-3

Lanthanum methoxypropylate 40.6 g (0.100 mol) Iron methoxypropylate 30.7g (0.095 mol)

The above listed components were charged in 1000 mL round bottomedflask, dissolved in 200 mL of toluene with stirring to obtain a mixedalkoxide solution. Separately, 1.52 g (0.005 mol) of palladiumacetylacetonate was dissolved in 20 mL of toluene, the resultingsolution was added to the mixed alkoxide solution in the round bottomedflask to obtain a homogeneous mixed solution containing LaFePd.

The homogeneous mixed solution was hydrolyzed by adding 200 mL ofdeionized water dropwise thereto over about fifteen minutes. Theresulting brown slurry was mixed with 24.5 g of the powdery lanthanumcontaining theta-alumina (containing 4.0% by weight of La₂O₃)(Production Example C2) with stirring at room temperature for two hours.Subsequently, the toluene and water were distilled off under reducedpressure, thereby to obtain a mixture of a pre-crystallizationcomposition of a LaFePd containing perovskite-type composite oxidehomogeneously dispersed in the lanthanum containing theta-alumina.

Next, the mixture was placed on a petri dish, subjected to forced airdrying at 60° C. for twenty four hours and heat treated in an electricfurnace at 800° C. in the air for one hour to obtain a powdery exhaustgas purifying catalyst comprising the lanthanum containing theta-aluminasupporting a La_(1.00)Fe_(0.95)Pd_(0.05)O₃ perovskite-type compositeoxide.

The resulting powder was prepared so as to have a weight ratio of theperovskite-type composite oxide to the lanthanum containingtheta-alumina of 1:1.

Example QA-4

Lanthanum methoxypropylate 40.6 g (0.100 mol) Iron methoxypropylate 18.4g (0.057 mol) Manganese methoxypropylate  8.9 g (0.038 mol)

The above listed components were charged in a 1000 mL round bottomedflask, dissolved in 200 mL of toluene with stirring to obtain a mixedalkoxide solution. Separately, 2.00 g (0.005 mol) of rhodiumacetylacetonate was dissolved in 20 mL of toluene, the resultingsolution was added to the mixed alkoxide solution in the round bottomedflask to obtain a homogeneous mixed solution containing LaFeMnRh.

The homogeneous mixed solution was hydrolyzed by adding 300 mL ofdeionized water dropwise thereto over about fifteen minutes. Afterstirring at room temperature for two hours, the toluene and water weredistilled off under reduced pressure, thereby to obtain apre-crystallization composition of a LaFeMnRh containing perovskite-typecomposite oxide. The pre-crystallization composition of LaFeMnRhcontaining perovskite-type composite oxide was charged in a 1000 mLround bottomed flask, was mixed with 200 mL of IPA (isopropyl alcohol)with stirring to obtain a slurry.

The resulting slurry was mixed with 220 g of the powdery lanthanumcontaining theta-alumina (containing 2.0% by weight of La₂O₃)(Production Example C1) with stirring at room temperature for one hour,IPA was distilled off therefrom under reduced pressure, thereby toobtain a mixture of a pre-crystallization composition of a LaFeMnRhcontaining perovskite-type composite oxide homogeneously dispersed inthe lanthanum containing theta-alumina.

Next, the mixture was placed on a petri dish, subjected to forced airdrying at 60° C. for twenty four hours and heat treated in an electricfurnace at 800° C. in the air for one hour to obtain a powdery exhaustgas purifying catalyst comprising the lanthanum containing theta-aluminasupporting a La_(1.00)Fe_(0.57)Mn_(0.38)Rh_(0.05)O₃ perovskite-typecomposite oxide.

The resulting powder was prepared so as to have a weight ratio of theperovskite-type composite oxide to the lanthanum containingtheta-alumina of 1:9.

Example QA-5

Lanthanum methoxypropylate 40.6 g (0.100 mol) Iron methoxypropylate 30.7g (0.095 mol)

The above listed components were charged in a 1000 mL round bottomedflask, dissolved in 200 mL of toluene with stirring to obtain a mixedalkoxide solution. Separately, 2.00 g (0.005 mol) of rhodiumacetylacetonate was dissolved in 20 mL of toluene, the resultingsolution was added to the mixed alkoxide solution in the round bottomedflask to obtain a LaFeRh containing homogeneous mixed solution.

Next, 36.8 g of the powdery lanthanum containing theta-alumina(containing 10.0% by weight of La₂O₃) (Production Example C3) was mixedwith the homogeneous mixed solution with stirring, and 200 mL ofdeionized water was added dropwise thereto over about fifteen minutes.As a result, a brown viscous precipitate was formed upon hydrolysis.

After stirring at room temperature for two hours, the toluene and waterwere distilled off under reduced pressure thereby to obtain a mixture ofa pre-crystallization composition of a LaFeRh containing perovskite-typecomposite oxide homogeneously dispersed in the lanthanum containingtheta-alumina. Next, the mixture was placed on a petri dish, subjectedto forced air drying at 60° C. for twenty four hours and heat treated inan electric furnace at 800° C. in the air for one hour to obtain apowdery exhaust gas purifying catalyst comprising the lanthanumcontaining theta-alumina supporting a La_(1.00)Fe_(0.95)Rh_(0.05)O₃perovskite-type composite oxide.

The resulting powder was prepared so as to have a weight ratio of theperovskite-type composite oxide to the lanthanum containingtheta-alumina of 2:3.

Example QA-6

Lanthanum methoxypropylate 38.6 g (0.095 mol) Iron methoxypropylate 18.4g (0.057 mol) Manganese methoxypropylate  8.9 g (0.038 mol)

The above listed components were charged in a 1000 mL round bottomedflask, dissolved in 200 mL of toluene with stirring to obtain a mixedalkoxide solution. Separately, 1.965 g (0.005 mol) of platinumacetylacetonate and 1.53 g (0.005 mol) of silver acetylacetonatedissolved in 40 mL of toluene, the resulting solution was added to themixed alkoxide solution in the round bottomed flask to obtain aLaAgFeMnPt containing homogeneous mixed solution.

Next, 24.5 g of the powdery lanthanum containing theta-alumina(containing 10.0% by weight of La₂O₃) (Production Example C3) was addedto the homogeneous mixed solution with stirring, and 200 mL of deionizedwater was added dropwise thereto over about fifteen minutes. As aresult, a brown viscous precipitate was formed upon hydrolysis.

After stirring at room temperature for two hours, the toluene and waterwere distilled off under reduced pressure, thereby to obtain a mixtureof a pre-crystallization composition of a LaAgFeMnPt containingperovskite-type composite oxide homogeneously dispersed in the lanthanumcontaining theta-alumina. Next, the mixture was placed on a petri dish,subjected to forced air drying at 60° C. for twenty four hours and heattreated in an electric furnace at 800° C. in the air for one hour toobtain a powdery exhaust gas purifying catalyst comprising the lanthanumcontaining theta-alumina supporting aLa_(0.95)Ag_(0.05)Fe_(0.57)Mn_(0.38)Pt_(0.05)O₃ perovskite-typecomposite oxide.

The resulting powder was prepared so as to have a weight ratio of theperovskite-type composite oxide to the lanthanum containingtheta-alumina of 1:1.

Example QA-7

Lanthanum methoxypropylate 36.6 g (0.090 mol) Calcium methoxypropylate 2.2 g (0.010 mol) Iron methoxypropylate 29.1 g (0.090 mol)

The above listed components were charged in a 1000 mL round bottomedflask, dissolved in 200 mL of toluene with stirring to obtain a mixedalkoxide solution. Separately, 3.93 g (0.010 mol) of platinumacetylacetonate was dissolved in 40 mL of toluene, the resultingsolution was added to the mixed alkoxide solution in the round bottomedflask to obtain a LaCaFePt containing homogeneous mixed solution.

Next, 98.7 g of the powdery theta-alumina was mixed with the homogeneousmixed solution with stirring, and 200 mL of deionized water was addeddropwise thereto over about fifteen minutes. As a result, a brownviscous precipitate was formed upon hydrolysis.

After stirring at room temperature for two hours, the toluene and waterwere distilled off under reduced pressure, thereby to obtain a mixtureof a pre-crystallization composition of a LaCaFePt containingperovskite-type composite oxide homogeneously dispersed in thetheta-alumina. Next, the mixture was placed on a petri dish, subjectedto forced air drying at 60° C. for twenty four hours and heat treated inan electric furnace at 800° C. in the air for one hour to obtain apowdery exhaust gas purifying catalyst comprising the theta-aluminasupporting a La_(0.09)Ca_(0.10)Fe_(0.90)Pt_(0.10)O₃ perovskite-typecomposite oxide.

The resulting powder was prepared so as to have a weight ratio of theperovskite-type composite oxide to the theta-alumina of 1:4.

Example QA-7-1

Lanthanum nitrate 43.3 g (0.100 mol) Iron nitrate 36.4 g (0.090 mol)

The above listed components were charged in a 1000 mL round bottomedflask, were homogeneously dissolved in 100 mL of deionized water toobtain an aqueous mixed salt solution. Next, 47.9 g (0.23 mol) of citricacid was dissolved in 100 mL of deionized water, the resulting solutionwas added to the aqueous mixed salt solution to obtain a LaFe containingaqueous citrate mixed salt solution.

Next, the aqueous citrate mixed salt solution was evaporated to drynessin a hot water bath at 60° C. to 80° C. while evacuating with a rotaryevaporator. At the time when the solution became viscous syrup afterabout three hour, the temperature of the hot water bath was graduallyraised, followed by vacuum drying at 300° C. for one hour, thereby toobtain a citrate complex.

The citrate complex was crushed in a mortar, baked at 350° C. in the airfor three hours and was placed again in the 1000 mL flask.

Separately, 3.05 g (0.010 mol) of palladium acetylacetonate wasdissolved in 200 mL of acetone, was charged in the round bottomed flask,followed by stirring, thereby to obtain a LaFePd containing homogenousmixed slurry.

Next, the acetone was distilled off from the homogeneous mixed slurry todryness. Separately, 24.5 g of the powdery lanthanum containingtheta-alumina (containing 4.0% by weight of La₂O₃) (Production ExampleC2) was dispersed in 100 mL of deionized water, and the resultingdispersion was charged in the round bottomed flask, followed bystirring.

After stirring at room temperature for two hours, the water wasdistilled off under reduced pressure, thereby to obtain a mixture of apre-crystallization composition of a LaFePd containing perovskite-typecomposite oxide homogeneously dispersed in the lanthanum containingtheta-alumina. Next, the lanthanum containing theta-alumina containingthe dispersed pre-crystallization composition was placed on a petridish, subjected to forced air drying at 60° C. for twenty four hours andheat treated in an electric furnace at 800° C. in the air for one hourto obtain a powdery lanthanum containing theta-alumina supporting aLa_(1.00)Fe_(0.90)Pd_(0.10)O₃ perovskite-type composite oxide.

The resulting powder was prepared so as to have a weight ratio of theperovskite-type composite oxide to the lanthanum containingtheta-alumina of 1:1.

Example QA-7-2

Lanthanum chloride 37.1 g (0.100 mol) Iron chloride 21.6 g (0.080 mol)

The above listed components were charged in a 1000 mL round bottomedflask, dissolved in 200 mL of deionized water to obtain an aqueous mixedsalt solution. Separately, 208 g of ammonium carbonate (containing 30%by weight of NH₃) was dissolved in 200 mL of deionized water to obtainan alkaline aqueous solution. The aqueous mixed salt solution wasgradually added dropwise thereto to form a coprecipitate. The reactionmixture was stirred at room temperature for two hours, and the resultingcoprecipitate was fully washed with water and filtrated.

Next, the coprecipitate was placed on a petri dish, was fully dried byforced air drying at 80° C. for twelve hours, was crushed in a mortarand was placed again in the 1000 mL flask.

Separately, 6.09 g (0.020 mol) of palladium acetylacetonate wasdissolved in 400 mL of acetone, the resulting solution was charged inthe round bottomed flask, followed by stirring, thereby to obtain aLaFePd containing homogenous mixed slurry.

Next, the acetone was distilled off from the homogeneous mixed slurry todryness. Separately, 24.5 g of the powdery lanthanum containingtheta-alumina (containing 4.0% by weight of La₂O₃) (Production ExampleC2) was dispersed in 100 mL of deionized water and the dispersion wascharged in the round bottomed flask, followed by stirring.

After stirring at room temperature for two hours, the water wasdistilled off under reduced pressure, thereby to obtain a mixture of apre-crystallization composition of a LaFePd containing perovskite-typecomposite oxide homogeneously dispersed in the lanthanum containingtheta-alumina. Next, the lanthanum containing theta-alumina containingthe dispersed pre-crystallization composition was placed on a petridish, subjected to forced air drying at 60° C. for twenty four hours andheat treated in an electric furnace at 800° C. in the air for one hourto obtain a powdery lanthanum containing theta-alumina supporting aLa_(1.00)Fe_(0.09)Pd_(0.10)O₃ perovskite-type composite oxide.

The resulting powder was prepared so as to have a weight ratio of theperovskite-type composite oxide to the lanthanum containingtheta-alumina of 1:1.

Example RA-8

1) Supporting of Palladium Containing Perovskite-Type Composite Oxide byThermostable Oxide

Lanthanum methoxypropylate 40.6 g (0.100 mol) Iron methoxypropylate 30.7g (0.095 mol)

The above listed components were charged in a 1000 mL round bottomedflask, dissolved in 200 mL of toluene with stirring to obtain a mixedalkoxide solution. Separately, 1.52 g (0.005 mol) of palladiumacetylacetonate was dissolved in 20 mL of toluene, the resultingsolution was added to the mixed alkoxide solution in the round bottomedflask to obtain a LaFePd containing homogeneous mixed solution.

Separately, the powdery lanthanum containing theta-alumina (containing4.0% by weight of La₂O₃) (Production Example C2) was dispersed in 200 mLof toluene and the homogeneous mixed solution in the round bottomedflask was added, followed by stirring.

Next, 200 mL of deionized water was added dropwise to the mixture overabout fifteen minutes. As a result, a brown viscous precipitate wasformed upon hydrolysis.

After stirring at room temperature for two hours, the toluene and waterwere distilled off under reduced pressure to obtain a lanthanumcontaining theta-alumina containing a pre-crystallization composition ofa LaFePd composite oxide dispersed therein. Next, the lanthanumcontaining theta-alumina containing the dispersed pre-crystallizationcomposition was placed on a petri dish, subjected to forced air dryingat 60° C. for twenty four hours and heat treated in an electric furnaceat 800° C. in the air for one hour to obtain a powdery lanthanumcontaining theta-alumina supporting a La_(1.00)Fe_(0.95)Pd_(0.05)O₃perovskite-type composite oxide.

The resulting powder was prepared so as to have a weight ratio of theperovskite-type composite oxide to the lanthanum containingtheta-alumina of 1:1.

2) Mixing of Perovskite-Type Composite Oxide with Thermostable Oxide andProduction of Exhaust Gas Purifying Catalyst

To the above prepared powdery lanthanum containing theta-aluminasupporting the perovskite-type composite oxide were added the powderyPt—Rh supporting zirconia composite oxide (Production Example A2-1)comprising a Zr_(0.76)Ce_(0.18)La_(0.02)Nd_(0.04) oxide supporting 1.00%by weight of Pt and 1.00% by weight of Rh, the powdery Pt supportingceria composite oxide (Production Example B1-1) comprising aCe_(0.60)Zr_(0.30)Y_(0.10) oxide supporting 1.00% by weight of Pt, andthe powdery Pt—Rh supporting theta-alumina (Production Example C6-1)comprising the theta-alumina supporting 0.57% by weight of Pt and 0.14%by weight of Rh. The mixture was mixed with deionized water, was furthermixed with alumina sol to obtain a slurry. The slurry was injected intoa honeycomb cordierite carrier having a size of 3 mil per 600 cells, adiameter of 86 mm and a length of 104 mm so as to homogeneously apply 30g of the lanthanum containing theta-alumina supporting theperovskite-type composite oxide, 30 g of the Pt—Rh supporting zirconiacomposite oxide, 80 g of the Pt supporting ceria composite oxide, and 70g of the Pt—Rh supporting theta-alumina per one liter of the honeycombcarrier. The resulting article dried at 100° C. and baked at 500° C. toobtain an exhaust gas purifying catalyst. The exhaust gas purifyingcatalyst contained 1.50 g of Pt, 0.33 g of Pd, and 0.40 g of Rh per oneliter of the honeycomb carrier.

Example RA-9

1) Supporting of Palladium Containing Perovskite-Type Composite Oxide byThermostable Oxide

Lanthanum methoxypropylate 40.6 g (0.100 mol) Iron methoxypropylate 30.7g (0.095 mol)

The above listed components were charged in a 1000 mL round bottomedflask, dissolved in 200 mL of toluene with stirring to obtain a mixedalkoxide solution. Separately, 1.52 g (0.005 mol) of palladiumacetylacetonate was dissolved in 20 mL of toluene, the resultingsolution was added to the mixed alkoxide solution in the round bottomedflask to obtain a LaFePd containing homogeneous mixed solution.

The homogeneous mixed solution was hydrolyzed by adding 200 mL ofdeionized water dropwise thereto over about fifteen minutes. Theresulting brown slurry was mixed with a dispersion of 24.5 g of thepowdery lanthanum containing theta-alumina (containing 4.0% by weight ofLa₂O₃) (Production Example C2) in 100 mL of deionized water. Afterstirring at room temperature for two hours, the toluene and water weredistilled off under reduced pressure, thereby to obtain a mixture of apre-crystallization composition of a LaFePd containing perovskite-typecomposite oxide homogeneously dispersed in the lanthanum containingtheta-alumina.

Next, the lanthanum containing theta-alumina containing the dispersedpre-crystallization composition (mixture) was placed on a petri dish,subjected to forced air drying at 60° C. for twenty four hours and heattreated in an electric furnace at 800° C. in the air for one hour toobtain a powdery lanthanum containing theta-alumina supporting aLa_(1.00)Fe_(0.95)Pd_(0.05)O₃ perovskite-type composite oxide.

The resulting powder was prepared so as to have a weight ratio of theperovskite-type composite oxide to the lanthanum containingtheta-alumina of 1:1.

2) Mixing of Zirconia Composite Oxide Supporting Perovskite-TypeComposite Oxide with Thermostable Oxide and Production of Exhaust GasPurifying Catalyst

To the above prepared powdery lanthanum containing theta-aluminasupporting the perovskite-type composite oxide were added the powdery Ptsupporting ceria composite oxide (Production Example B1-1) comprising aCe_(0.60)Zr_(0.30)Y_(0.10) oxide supporting 1.00% by weight of Pt, andthe powdery Pt—Rh supporting gamma-alumina (Production Example D1)comprising a gamma-alumina supporting 1.00% by weight of Pt and 0.57% byweight of Rh. The resulting mixture was mixed with deionized water andwas then mixed with alumina sol to form a slurry. The slurry wasinjected into a honeycomb cordierite carrier having a size of 3 mil per600 cells, a diameter of 86 mm and a length of 104 mm so as tohomogeneously apply 30 g of the lanthanum containing theta-aluminasupporting the perovskite-type composite oxide, 80 g of the Ptsupporting ceria composite oxide, and 70 g of the Pt—Rh supportinggamma-alumina per one liter of the honeycomb carrier. The resultingarticle dried at 100° C. and baked at 500° C. to obtain an exhaust gaspurifying catalyst. The exhaust gas purifying catalyst contained 1.50 gof Pt, 0.33 g of Pd, and 0.40 g of Rh per one liter of the honeycombcarrier.

Example RA-9-1

1) Supporting of Palladium Containing Perovskite-Type Composite Oxide byThermostable Oxide

Lanthanum methoxypropylate 40.6 g (0.100 mol) Iron methoxypropylate 30.7g (0.095 mol)

The above listed components were charged in a 1000 mL round bottomedflask, dissolved in 200 mL of toluene with stirring to obtain a mixedalkoxide solution. Separately, 1.52 g (0.005 mol) of palladiumacetylacetonate was dissolved in 20 mL of toluene, the resultingsolution was added to the mixed alkoxide solution in the round bottomedflask to obtain a LaFePd containing homogeneous mixed solution.

A powdery alpha-alumina was dispersed in 200 mL of toluene and thehomogeneous mixed solution in the round bottomed flask was added,followed by stirring.

Next, 200 mL of deionized water was added dropwise to the mixture overabout fifteen minutes. As a result, a brown viscous precipitate wasformed upon hydrolysis.

After stirring at room temperature for two hours, the toluene and waterwere distilled off under reduced pressure to obtain a mixture ofalpha-alumina containing a dispersed pre-crystallization composition ofa LaFePd composite oxide. Next, the alpha-alumina with the dispersedpre-crystallization composition (mixture) was placed on a petri dish,subjected to forced air drying at 60° C. for twenty four hours and heattreated in an electric furnace at 800° C. in the air for one hour toobtain a powdery alpha-alumina supporting aLa_(1.00)Fe_(0.95)Pd_(0.05)O₃ perovskite-type composite oxide.

The resulting powder was prepared so as to have a weight ratio of theperovskite-type composite oxide to the alpha-alumina of 1:2.

2) Mixing of Perovskite-Type Composite Oxide with Thermostable Oxide andProduction of Exhaust Gas Purifying Catalyst

To the powdery alpha-alumina supporting the perovskite-type compositeoxide were added the powdery Pt—Rh supporting zirconia composite oxide(Production Example A2-1) comprising aZr_(0.76)Ce_(0.18)La_(0.02)Nd_(0.04) oxide supporting 1.00% by weight ofPt and 1.00% by weight of Rh, the powdery Pt supporting ceria compositeoxide (Production Example B1-4) comprising a Ce_(0.60)Zr_(0.30)Y_(0.10)oxide supporting 1.38% by weight of Pt, and a powdery gamma-alumina. Theresulting mixture was mixed with deionized water and was then mixed withalumina sol to form a slurry. The slurry was charged into a honeycombcordierite carrier having a size of 3 mil per 600 cells, a diameter of86 mm and a length of 104 mm so as to homogeneously apply 45 g of thealpha-alumina supporting the perovskite-type composite oxide, 40 g ofthe Pt—Rh supporting zirconia composite oxide, 80 g of the Pt supportingceria composite oxide, and 70 g of the gamma-alumina per one liter ofthe honeycomb carrier. The resulting article dried at 100° C. and bakedat 500° C. to obtain an exhaust gas purifying catalyst. The exhaust gaspurifying catalyst contained 1.50 g of Pt, 0.33 g of Pd, and 0.40 g ofRh per one liter of the honeycomb carrier.

Example RC-10

1) Formation of Inner Layer

1) -1 Supporting of Palladium Containing Perovskite-Type Composite Oxideby Thermostable Oxide

Lanthanum methoxypropylate 40.6 g (0.100 mol) Iron methoxypropylate 30.7g (0.095 mol)

The above listed components were charged in a 1000 mL round bottomedflask, dissolved in 200 mL of toluene with stirring to obtain a mixedalkoxide solution. Separately, 1.52 g (0.005 mol) of palladiumacetylacetonate was dissolved in 100 mL of toluene, the resultingsolution was added to the mixed alkoxide solution in the round bottomedflask to obtain a LaFePd containing homogeneous mixed solution.

Separately, the powdery lanthanum containing theta-alumina (containing4.0% by weight of La₂O₃) (Production Example C2) was dispersed in 200 mLof toluene and the homogeneous mixed solution in the round bottomedflask was added, followed by stirring.

Next, 200 mL of deionized water was added dropwise to the mixture overabout fifteen minutes. As a result, a brown viscous precipitate wasformed upon hydrolysis.

After stirring at room temperature for two hours, the toluene and waterwere distilled off under reduced pressure to obtain a mixture of alanthanum containing theta-alumina with a dispersed pre-crystallizationcomposition of a LaFePd composite oxide. Next, the lanthanum containingtheta-alumina with the dispersed pre-crystallization composition(mixture) was placed on a petri dish, subjected to forced air drying at60° C. for twenty four hours and heat treated in an electric furnace at650° C. in the air for one hour to obtain a powdery lanthanum containingtheta-alumina supporting a La_(1.00)Fe_(0.95)Pd_(0.05)O₃ perovskite-typecomposite oxide.

The resulting powder was prepared so as to have a weight ratio of theperovskite-type composite oxide to the lanthanum containingtheta-alumina of 1:1.

1) -2 Production of Inner Layer

To the above prepared powdery lanthanum containing theta-aluminasupporting the palladium containing perovskite-type composite oxide wereadded the powdery Pt supporting ceria composite oxide (ProductionExample B1-2) comprising a Ce_(0.60)Zr_(0.30)Y_(0.10) oxide supporting0.33% by weight of Pt, and the powdery theta-alumina. The resultingmixture was further mixed with deionized water and then mixed withalumina sol to form a slurry. The slurry was injected into a honeycombcordierite carrier having a size of 3 mil per 600 cells, a diameter of86 mm and a length of 104 mm so as to homogeneously apply 28 g of thelanthanum containing theta-alumina supporting the palladium containingperovskite-type composite oxide, 60 g of the Pt supporting ceriacomposite oxide, and 70 g of the theta-alumina per one liter of thehoneycomb carrier. The resulting article dried at 100° C. and baked at500° C. to form an inner layer.

2) Production of Outer Layer and Exhaust Gas Purifying Catalyst

The powdery Pt—Rh supporting zirconia composite oxide (ProductionExample A2-2) comprising a Zr_(0.76)Ce_(0.18)La_(0.02)Nd_(0.04) oxidesupporting 0.27% by weight of Pt and 1.33% by weight of Rh, the powderyPt supporting ceria composite oxide (Production Example B1-2) comprisinga Ce_(0.60)Zr_(0.30)Y_(0.10) oxide supporting 0.33% by weight of Pt, andthe powdery Pt supporting theta-alumina (Production Example C5)comprising the theta-alumina supporting 0.31% by weight of Pt weremixed. The resulting mixture was further mixed with deionized water andthen mixed with alumina sol to form a slurry. The slurry was chargedinto the honeycomb cordierite carrier having a size of 3 mil per 600cells, a diameter of 86 mm and a length of 104 mm so as to homogeneouslyapply, to a surface of the inner layer, 30 g of the Pt—Rh supportingzirconia composite oxide, 60 g of the Pt supporting ceria compositeoxide, and 70 g of the Pt supporting theta-alumina per one liter of thehoneycomb carrier. The resulting article dried at 100° C. and baked at500° C. to form an outer layer. Thus, an exhaust gas purifying catalystwas produced.

The exhaust gas purifying catalyst contained 0.10 g of Pt and 0.30 g ofPd in the inner layer, and 0.50 g of Pt and 0.40 g of Rh in the outerlayer, respectively, per one liter of the honeycomb carrier.

Example RC-11

1) Formation of Inner Layer

1) -1 Supporting of Palladium Containing Perovskite-Type Composite Oxideby Thermostable Oxide

Lanthanum methoxypropylate 40.6 g (0.100 mol) Iron methoxypropylate 30.7g (0.095 mol)

The above listed components were charged in a 1000 mL round bottomedflask, dissolved in 200 mL of toluene with stirring to obtain a mixedalkoxide solution. Separately, 1.52 g (0.005 mol) of palladiumacetylacetonate was dissolved in 100 mL of toluene, the resultingsolution was added to the mixed alkoxide solution in the round bottomedflask to obtain a LaFePd containing homogeneous mixed solution.

The homogeneous mixed solution was hydrolyzed by adding 200 mL ofdeionized water dropwise thereto over about fifteen minutes. Theresulting brown slurry was mixed with a dispersion of 24.5 g of thepowdery lanthanum containing theta-alumina (containing 4.0% by weight ofLa₂O₃) (Production Example C2) in 100 mL of deionized water. Afterstirring at room temperature for two hours, the toluene and water weredistilled off under reduced pressure, thereby to obtain a mixture of apre-crystallization composition of a LaFePd containing perovskite-typecomposite oxide homogeneously dispersed in the lanthanum containingtheta-alumina.

Next, the lanthanum containing theta-alumina with the dispersedpre-crystallization composition (mixture) was placed on a petri dish,subjected to forced air drying at 60° C. for twenty four hours and heattreated in an electric furnace at 650° C. in the air for one hour toobtain a powdery lanthanum containing theta-alumina supporting aLa_(1.00)Fe_(0.95)Pd_(0.05)O₃ perovskite-type composite oxide.

The resulting powder was prepared so as to have a weight ratio of theperovskite-type composite oxide to the lanthanum containingtheta-alumina of 1:1.

1) -2 Production of Inner Layer

To the above prepared powdery lanthanum containing theta-aluminasupporting the palladium containing perovskite-type composite oxide wereadded the powdery Pt supporting ceria composite oxide (ProductionExample B1-3) comprising a Ce_(0.60)Zr_(0.30)Y_(0.10) oxide supporting0.67% by weight of Pt, and the powdery theta-alumina. The resultingmixture was further mixed with deionized water and then mixed withalumina sol to form a slurry. The slurry was injected into a honeycombcordierite carrier having a size of 3 mil per 600 cells, a diameter of86 mm and a length of 104 mm so as to homogeneously apply 30 g of thelanthanum containing theta-alumina supporting the palladium containingperovskite-type composite oxide, 30 g of the Pt supporting ceriacomposite oxide, and 80 g of the theta-alumina per one liter of thehoneycomb carrier. The resulting article dried at 100° C. and baked at500° C. to form an inner layer.

2) Production of Outer Layer and Exhaust Gas Purifying Catalyst

The powdery Pt—Rh supporting zirconia composite oxide (ProductionExample A1-1) comprising a Zr_(0.50)Ce_(0.40)La_(0.05)Nd_(0.05) oxidesupporting 0.27% by weight of Pt and 1.33% by weight of Rh was mixedwith the powdery Pt supporting ceria composite oxide (Production ExampleB1-2) comprising a Ce_(0.60)Zr_(0.30)Y_(0.10) oxide supporting 0.33% byweight of Pt, and the powdery Pt—Rh supporting theta-alumina (ProductionExample C6-2) comprising a theta-alumina supporting 0.43% by weight ofPt and 0.21% by weight of Rh. The resulting mixture was further mixedwith deionized water and then mixed with alumina sol to form a slurry.The slurry was injected into a honeycomb cordierite carrier having asize of 3 mil per 600 cells, a diameter of 86 mm and a length of 104 mm,thereby to homogeneously apply, to a surface of the inner layer, 30 g ofthe Pt—Rh supporting zirconia composite oxide, 60 g of the Pt supportingceria composite oxide, and 70 g of the Pt—Rh supporting theta-aluminaper one liter of the honeycomb carrier. The resulting article dried at100° C. and baked at 500° C. to form an outer layer. Thus, an exhaustgas purifying catalyst was produced.

The exhaust gas purifying catalyst contained 0.20 g of Pt and 0.33 g ofPd in the inner layer, and 0.58 g of Pt and 0.55 g of Rh in the outerlayer, respectively, per one liter of the honeycomb carrier.

Example RC-12

1) Formation of Inner Layer

1) -1 Supporting of Palladium Containing Perovskite-Type Composite Oxideby Thermostable Oxide

Lanthanum methoxypropylate 40.6 g (0.100 mol) Iron methoxypropylate 30.7g (0.095 mol)

The above listed components were charged in a 1000 mL round bottomedflask, dissolved in 200 mL of toluene with stirring to obtain a mixedalkoxide solution. Separately, 1.52 g (0.005 mol) of palladiumacetylacetonate was dissolved in 100 mL of toluene, the resultingsolution was added to the mixed alkoxide solution in the round bottomedflask to obtain a LaFePd containing homogeneous mixed solution.

Separately, the powdery barium containing theta-alumina (containing 4.0%by weight of BaO) (Production Example C4) was dispersed in 200 mL oftoluene and the homogeneous mixed solution in the round bottomed flaskwas added, followed by stirring.

Next, 200 mL of deionized water was added dropwise to the mixture overabout fifteen minutes. As a result, a brown viscous precipitate wasformed upon hydrolysis.

After stirring at room temperature for two hours, the toluene and waterwere distilled off under reduced pressure to obtain a mixture of abarium containing theta-alumina with a dispersed pre-crystallizationcomposition of a LaFePd composite oxide. Next, the barium containingtheta-alumina with the dispersed pre-crystallization composition(mixture) was placed on a petri dish, subjected to forced air drying at60° C. for twenty four hours and heat treated in an electric furnace at650° C. in the air for one hour to obtain a powdery barium containingtheta-alumina supporting a La_(1.00)Fe_(0.95)Pd_(0.05)O₃ perovskite-typecomposite oxide.

The resulting powder was prepared so as to have a weight ratio of theperovskite-type composite oxide to the barium containing theta-aluminaof 1:4.

1) -2 Production of Inner Layer

To the above prepared powdery barium containing theta-alumina supportingthe palladium containing perovskite-type composite oxide was added thepowdery Pt supporting ceria composite oxide (Production Example B1-3)comprising a Ce_(0.60)Zr_(0.30)Y_(0.10) oxide supporting 0.67% by weightof Pt. The resulting mixture was further mixed with deionized water andthen mixed with alumina sol to form a slurry. The slurry was injectedinto a honeycomb cordierite carrier having a size of 3 mil per 600cells, a diameter of 86 mm and a length of 104 mm so as to homogeneouslyapply 46 g of the barium containing theta-alumina supporting thepalladium containing perovskite-type composite oxide and 45 g of the Ptsupporting ceria composite oxide per one liter of the honeycomb carrier.The resulting article dried at 100° C. and baked at 500° C. to form aninner layer.

2) Formation of Outer Layer

2) -1 Supporting of Rhodium Containing Perovskite-Type Composite Oxideby Thermostable Oxide

Lanthanum methoxypropylate 40.6 g (0.100 mol) Iron methoxypropylate 30.7g (0.095 mol)

The above listed components were charged in a 1000 mL round bottomedflask, dissolved in 200 mL of toluene with stirring to obtain a mixedalkoxide solution. Separately, 2.00 g (0.005 mol) of rhodiumacetylacetonate was dissolved in 100 mL of toluene, the resultingsolution was added to the mixed alkoxide solution in the round bottomedflask to obtain a LaFeRh containing homogeneous mixed solution.

Separately, the powdery theta-alumina was dispersed in 200 mL of tolueneand the homogeneous mixed solution in the round bottomed flask wasadded, followed by stirring.

Next, 200 mL of deionized water was added dropwise to the mixture overabout fifteen minutes. As a result, a brown viscous precipitate wasformed upon hydrolysis.

After stirring at room temperature for two hours, the toluene and waterwere distilled off under reduced pressure to obtain a mixture of atheta-alumina with a dispersed pre-crystallization composition of aLaFePd composite oxide. Next, the theta-alumina with the dispersedpre-crystallization composition (mixture) was placed on a petri dish,subjected to forced air drying at 60° C. for twenty four hours and heattreated in an electric furnace at 650° C. in the air for one hour toobtain a powdery theta-alumina supporting aLa_(1.00)Fe_(0.95)Rh_(0.05)O₃ perovskite-type composite oxide.

The resulting powder was prepared so as to have a weight ratio of theperovskite-type composite oxide to the theta-alumina of 1:3.

2) -2 Production of Outer Layer and Exhaust Gas Purifying Catalyst

To the above prepared powdery theta-alumina supporting the rhodiumcontaining perovskite-type composite oxide was added the powdery Ptsupporting ceria composite oxide (Production Example B1-3) comprising aCe_(0.60)Zr_(0.30)Y_(0.10) oxide supporting 0.67% by weight of Pt. Theresulting mixture was further mixed with deionized water and then mixedwith alumina sol to form a slurry. The slurry was injected into ahoneycomb cordierite carrier having a size of 3 mil per 600 cells, adiameter of 86 mm and a length of 104 mm so as to homogeneously apply,to a surface of the inner layer, 38 g of the theta-alumina supportingthe rhodium containing perovskite-type composite oxide and 60 g of thePt supporting ceria composite oxide per one liter of the honeycombcarrier. The resulting article dried at 100° C. and baked at 500° C. toform an outer layer. Thus, an exhaust gas purifying catalyst wasproduced.

The exhaust gas purifying catalyst contained 0.30 g of Pt and 0.20 g ofPd in the inner layer, and 0.40 g of Pt and 0.20 g of Rh in the outerlayer, respectively, per one liter of the honeycomb carrier.

Example RC-13

1) Formation of Inner Layer

1) -1 Supporting of Palladium Containing Perovskite-Type Composite Oxideby Thermostable Oxide

Lanthanum methoxypropylate 40.6 g (0.100 mol) Iron methoxypropylate 30.7g (0.095 mol)

The above listed components were charged in a 1000 mL round bottomedflask, dissolved in 200 mL of toluene with stirring to obtain a mixedalkoxide solution. Separately, 1.52 g (0.005 mol) of palladiumacetylacetonate was dissolved in 100 mL of toluene, the resultingsolution was added to the mixed alkoxide solution in the round bottomedflask to obtain a LaFePd containing homogeneous mixed solution.

To the homogeneous mixed solution was added 200 mL of deionized waterdropwise over about fifteen minutes. After stirring at room temperaturefor two hours, the toluene and water were distilled off under reducedpressure, thereby to obtain a pre-crystallization composition of aLaFePd containing perovskite-type composite oxide. Thepre-crystallization composition of LaFePd containing perovskite-typecomposite oxide was charged in a 1000 mL round bottomed flask and wasmixed with 200 mL of IPA (isopropyl alcohol) with stirring to form aslurry. The resulting slurry was mixed with 24.5 g of a powderyalpha-alumina, was stirring at room temperature for one hour, and IPAwas distilled off under reduced pressure, thereby to obtain a mixture ofa pre-crystallization composition of a LaFePd containing perovskite-typecomposite oxide homogeneously dispersed in the alpha-alumina.

Next, the alpha-alumina with the dispersed pre-crystallizationcomposition (mixture) was placed on a petri dish, subjected to forcedair drying at 60° C. for twenty four hours and heat treated in anelectric furnace at 650° C. in the air for one hour to obtain a powderyalpha-alumina supporting a La_(1.00)Fe_(0.95)Pd_(0.05)O₃ perovskite-typecomposite oxide.

The resulting powder was prepared so as to have a weight ratio of theperovskite-type composite oxide to the alpha-alumina of 2:3.

1) -2 Production of Inner Layer

To the above prepared powdery alpha-alumina supporting the palladiumcontaining perovskite-type composite oxide were added the powdery Ptsupporting ceria composite oxide (Production Example B1-2) comprising aCe_(0.60)Zr_(0.30)Y_(0.10) oxide supporting 0.33% by weight of Pt andthe powdery theta-alumina. The resulting mixture was further mixed withdeionized water and then mixed with alumina sol to form a slurry. Theslurry was injected into a honeycomb cordierite carrier having a size of3 mil per 600 cells, a diameter of 86 mm and a length of 104 mm so as tohomogeneously apply 40 g of the alpha-alumina supporting the palladiumcontaining perovskite-type composite oxide, 30 g of the Pt supportingceria composite oxide, and 80 g of the theta-alumina per one liter ofthe honeycomb carrier. The resulting article dried at 100° C. and bakedat 500° C. to form an inner layer.

2) Formation of Outer Layer

2) -1 Supporting of Platinum Containing Perovskite-Type Composite Oxideby Thermostable Oxide

Lanthanum methoxypropylate 38.6 g (0.090 mol) Calcium methoxypropylate 2.2 g (0.010 mol) Iron methoxypropylate 29.1 g (0.090 mol)

The above listed components were charged in a 1000 mL round bottomedflask, dissolved in 200 mL of toluene with stirring to obtain a mixedalkoxide solution. Separately, 3.93 g (0.010 mol) of platinumacetylacetonate was dissolved in 40 mL of toluene, the resultingsolution was added to the mixed alkoxide solution in the round bottomedflask to obtain a LaCaFePt containing homogeneous mixed solution.

Separately, the powdery theta-alumina was dispersed in 200 mL of tolueneand the homogeneous mixed solution in the round bottomed flask wasadded, followed by stirring.

Next, 200 mL of deionized water was added dropwise to the mixture overabout fifteen minutes. As a result, a brown viscous precipitate wasformed upon hydrolysis.

After stirring at room temperature for two hours, the toluene and waterwere distilled off under reduced pressure to obtain a mixture of atheta-alumina with a dispersed pre-crystallization composition of aLaCaFePt composite oxide. Next, the theta-alumina with the dispersedpre-crystallization composition (mixture) was placed on a petri dish,subjected to forced air drying at 60° C. for twenty four hours and heattreated in an electric furnace at 650° C. in the air for one hour toobtain a powdery theta-alumina supporting aLa_(0.90)Ca_(0.10)Fe_(0.90)Pt_(0.10)O₃ perovskite-type composite oxide.

The resulting powder was prepared so as to have a weight ratio of theperovskite-type composite oxide to the theta-alumina of 2:3.

2) -2 Production of Outer Layer and Exhaust Gas Purifying Catalyst

To the above prepared powdery theta-alumina supporting the platinumcontaining perovskite-type composite oxide were added the powdery Pt—Rhsupporting zirconia composite oxide (Production Example A4-1) comprisinga Zr_(0.70)Ce_(0.25)La_(0.02)Nd_(0.03) oxide supporting 0.75% by weightof Pt and 1.25% by weight of Rh, and the powdery Pt supporting ceriacomposite oxide (Production Example B1-2) comprising aCe_(0.60)Zr_(0.30)Y_(0.10) oxide supporting 0.33% by weight of Pt. Theresulting mixture was further mixed with deionized water and then mixedwith alumina sol to form a slurry. The slurry was charged into ahoneycomb cordierite carrier having a size of 3 mil per 600 cells, adiameter of 86 mm and a length of 104 mm so as to homogeneously apply,to a surface of the inner layer, 3.2 g of the theta-alumina supportingthe platinum containing perovskite-type composite oxide, 40 g of thePt—Rh supporting zirconia composite oxide, and 60 g of the Pt supportingceria composite oxide per one liter of the honeycomb carrier. Theresulting article dried at 100° C. and baked at 500° C. to form an outerlayer. Thus, an exhaust gas purifying catalyst was produced.

The exhaust gas purifying catalyst contained 0.10 g of Pt and 0.35 g ofPd in the inner layer, and 0.60 g of Pt and 0.50 g of Rh in the outerlayer, respectively, per one liter of the honeycomb carrier.

Comparative Example QX-1

Lanthanum ethoxyethylate 40.6 g (0.100 mol) Iron ethoxyethylate 30.7 g(0.095 mol)

The above listed components were charged in a 1000 mL round bottomedflask, dissolved in 200 mL of toluene with stirring to obtain a mixedalkoxide solution. Separately, 1.52 g (0.005 mol) of palladiumacetylacetonate was dissolved in 100 mL of toluene, the resultingsolution was added to the mixed alkoxide solution in the round bottomedflask to obtain a LaFePd containing homogeneous mixed solution.

Next, the powdery zirconia composite oxide (Production Example A5)comprising a Zr_(0.70)Ce_(0.25)La_(0.02)Y_(0.03) oxide was dissolved in200 mL of toluene, and the resulting solution was added to thehomogeneous mixed solution in the round bottomed flask with stirring.

Next, 200 mL of deionized water was added dropwise to the mixture overabout fifteen minutes. As a result, a brown viscous precipitate wasformed upon hydrolysis.

After stirring at room temperature for two hours, the toluene and waterwere distilled off under reduced pressure to obtain a mixture of azirconia composite oxide with a dispersed pre-crystallizationcomposition of a LaFePd composite oxide. Next, the zirconia compositeoxide with the dispersed pre-crystallization composition (mixture) wasplaced on a petri dish, subjected to forced air drying at 60° C. fortwenty four hours and heat treated in an electric furnace at 650° C. inthe air for one hour to obtain a powdery exhaust gas purifying catalystcomprising a Zr_(0.70)Ce_(0.25)La_(0.02)Y_(0.03) oxide zirconiacomposite oxide supporting a La_(1.00)Fe_(0.95)Pd_(0.05)O₃perovskite-type composite oxide.

The resulting powder was prepared so as to have a weight ratio of theperovskite-type composite oxide to the zirconia composite oxide of 1:4.

Comparative Example QX-2

Lanthanum ethoxyethylate 40.6 g (0.100 mol) Iron ethoxyethylate 30.7 g(0.095 mol)

The above listed components were charged in a 1000 mL round bottomedflask, dissolved in 200 mL of toluene with stirring to obtain a mixedalkoxide solution. Separately, 2.00 g (0.005 mol) of rhodiumacetylacetonate was dissolved in 100 mL of toluene, the resultingsolution was added to the mixed alkoxide solution in the round bottomedflask to obtain a LaFeRh containing homogeneous mixed solution.

Separately, the powdery zirconia composite oxide (Production Example A3)comprising a Zr_(0.50)Ce_(0.40)La_(0.05)Y_(0.05) oxide was dissolved in100 mL of toluene and the homogeneous mixed solution in the roundbottomed flask was added, followed by stirring.

Next, 200 mL of deionized water was added dropwise to the mixture overabout fifteen minutes. As a result, a brown viscous precipitate wasformed upon hydrolysis.

After stirring at room temperature for two hours, the toluene and waterwere distilled off under reduced pressure to obtain a mixture of azirconia composite oxide with a dispersed pre-crystallizationcomposition of a LaFeRh composite oxide. Next, the zirconia compositeoxide with the dispersed pre-crystallization composition (mixture) wasplaced on a petri dish, subjected to forced air drying at 60° C. fortwenty four hours and heat treated in an electric furnace at 650° C. inthe air for one hour to obtain a powdery exhaust gas purifying catalystcomprising a Zr_(0.50)Ce_(0.40)La_(0.05)Y_(0.05) oxide zirconiacomposite oxide supporting a La_(1.00)Fe_(0.95)Rh_(0.05)O₃perovskite-type composite oxide.

The resulting powder was prepared so as to have a weight ratio of theperovskite-type composite oxide to the zirconia composite oxide of 2:3.

Comparative Example QX-3

Lanthanum methoxypropylate 36.6 g (0.090 mol) Calcium methoxypropylate 2.2 g (0.010 mol) Iron methoxypropylate 29.1 g (0.090 mol)

The above listed components were charged in a 1000 mL round bottomedflask, dissolved in 200 mL of toluene with stirring to obtain a mixedalkoxide solution. Separately, 3.93 g (0.010 mol) of platinumacetylacetonate was dissolved in 100 mL of toluene, the resultingsolution was added to the mixed alkoxide solution in the round bottomedflask to obtain a LaCaFePt containing homogeneous mixed solution.

Separately, the powdery zirconia composite oxide (Production Example A6)comprising a Zr_(0.70)Ce_(0.25)Pr_(0.02)Nd_(0.03) oxide was dispersed in100 mL of toluene and the homogeneous mixed solution in the roundbottomed flask was added, followed by stirring.

Next, 200 mL of deionized water was added dropwise to the mixture overabout fifteen minutes. As a result, a brown viscous precipitate wasformed upon hydrolysis.

After stirring at room temperature for two hours, the toluene and waterwere distilled off under reduced pressure, thereby to obtain a mixtureof a zirconia composite oxide with a dispersed pre-crystallizationcomposition of a LaCaFePt containing perovskite-type composite oxide.Next, the zirconia composite oxide with the dispersedpre-crystallization composition (mixture) was placed on a petri dish,subjected to forced air drying at 60° C. for twenty four hours and heattreated in an electric furnace at 800° C. in the air for one hour toobtain a powdery exhaust gas purifying catalyst comprising aZr_(0.70)Ce_(0.25)Pr_(0.02)Nd_(0.03) oxide zirconia composite oxidesupporting a La_(0.90)Ca_(0.10)Fe_(0.90)Pt_(0.10)O₃ perovskite-typecomposite oxide.

The resulting powder was prepared so as to have a weight ratio of theperovskite-type composite oxide to the zirconia composite oxide of 1:4.

Comparative Example QX-4

Lanthanum ethoxyethylate 40.6 g (0.100 mol) Iron ethoxyethylate 30.7 g(0.095 mol)

The above listed components were charged in a 1000 mL round bottomedflask, dissolved in 200 mL of toluene with stirring to obtain a mixedalkoxide solution. Separately, 1.52 g (0.005 mol) of palladiumacetylacetonate was dissolved in 100 mL of toluene, the resultingsolution was added to the mixed alkoxide solution in the round bottomedflask to obtain a LaFePd containing homogeneous mixed solution.

The homogeneous mixed solution was hydrolyzed by adding 200 mL ofdeionized water dropwise thereto over about fifteen minutes. Theresulting brown slurry was mixed with a dispersion of 98.0 g of apowdery gamma-alumina in 200 mL of deionized water. After stirring atroom temperature for two hours, the toluene and water were distilled offunder reduced pressure, thereby to obtain a mixture of a gamma-aluminawith a dispersed pre-crystallization composition of a LaFePd containingperovskite-type composite oxide.

Next, the gamma-alumina with the dispersed pre-crystallizationcomposition (mixture) was placed on a petri dish, subjected to forcedair drying at 60° C. for twenty four hours and heat treated in anelectric furnace at 650° C. in the air for one hour to obtain a powderyexhaust gas purifying catalyst comprising a gamma-alumina supporting aLa_(1.00)Fe_(0.95)Pd_(0.05)O₃ perovskite-type composite oxide.

The resulting powder was prepared so as to have a weight ratio of theperovskite-type composite oxide to the gamma-alumina of 1:4.

Comparative Example RX-5

The powdery Pd supporting theta-alumina (Production Example C7)comprising a theta-alumina supporting 1.10% by weight of Pd was mixedwith the powdery Pt supporting ceria composite oxide (Production ExampleB1-5) comprising a Ce_(0.60)Zr_(0.30)Y_(0.10) oxide supporting 1.50% byweight of Pt, and the powdery Pt—Rh supporting theta-alumina (ProductionExample C6-3) comprising a theta-alumina supporting 1.50% by weight ofPt and 0.67% by weight of Rh. The resulting mixture was mixed withdeionized water and was then mixed with alumina sol to form a slurry.The slurry was injected into a honeycomb cordierite carrier having asize of 3 mil per 600 cells, a diameter of 86 mm and a length of 104 mmso as to homogeneously apply 30 g of the Pd supporting theta-alumina, 40g of the Pt supporting ceria composite oxide, and 60 g of the Pt—Rhsupporting theta-alumina per one liter of the honeycomb carrier. Theresulting article dried at 100° C. and baked at 500° C. to obtain anexhaust gas purifying catalyst. The exhaust gas purifying catalystcontained 1.50 g of Pt, 0.33 g of Pd, and 0.40 g of Rh, per one liter ofthe honeycomb carrier.

Comparative Example RX-6

1) Formation of Inner Layer

1) -1 Supporting of Palladium Containing Perovskite-Type Composite Oxideby Thermostable Oxide

Lanthanum ethoxyethylate 40.6 g (0.100 mol) Iron ethoxyethylate 30.7 g(0.095 mol)

The above listed components were charged in a 1000 mL round bottomedflask, dissolved in 200 mL of toluene with stirring to obtain a mixedalkoxide solution. Separately, 1.52 g (0.005 mol) of palladiumacetylacetonate was dissolved in 100 mL of toluene, the resultingsolution was added to the mixed alkoxide solution in the round bottomedflask to obtain a LaFePd containing homogeneous mixed solution.

The homogeneous mixed solution was hydrolyzed by adding 200 mL ofdeionized water dropwise thereto over about fifteen minutes. Theresulting brown slurry was mixed with a dispersion of a powderygamma-alumina in 200 mL of deionized water. After stirring at roomtemperature for two hours, the toluene and water were distilled offunder reduced pressure, thereby to obtain a mixture of a gamma-aluminawith a dispersed pre-crystallization composition of a LaFePd containingperovskite-type composite oxide.

Next, the gamma-alumina with the dispersed pre-crystallizationcomposition (mixture) was placed on a petri dish, subjected to forcedair drying at 60° C. for twenty four hours and heat treated in anelectric furnace at 650° C. in the air for one hour to obtain a powderygamma-alumina supporting a La_(1.00)Fe_(0.95)Pd_(0.05)O₃ perovskite-typecomposite oxide.

The resulting powder was prepared so as to have a weight ratio of theperovskite-type composite oxide to the gamma-alumina of 1:1.

1) -2 Production of Inner Layer

To the above prepared powdery gamma-alumina supporting the palladiumcontaining perovskite-type composite oxide was added a powderygamma-alumina. The resulting mixture was further mixed with deionizedwater and then mixed with alumina sol to form a slurry. The slurry wasinjected into a honeycomb cordierite carrier having a size of 3 mil per600 cells, a diameter of 86 mm and a length of 104 mm so as tohomogeneously apply 60 g of the gamma-alumina supporting the palladiumcontaining perovskite-type composite oxide and 30 g of the gamma-aluminaper one liter of the honeycomb carrier. The resulting article dried at100° C. and baked at 500° C. to form an inner layer.

2) Production of Outer Layer and Exhaust Gas Purifying Catalyst

To the powdery Pt—Rh supporting ceria composite oxide (ProductionExample B2-1) comprising a Ce_(0.30)Zr_(0.70)O₂ supporting 2.00% byweight of Pt and 1.00% by weight of Rh was added a powderygamma-alumina. The resulting mixture was further mixed with deionizedwater and then mixed with alumina sol to form a slurry. The slurry wascharged into a honeycomb cordierite carrier having a size of 3 mil per600 cells, a diameter of 86 mm and a length of 104 mm so as tohomogeneously apply, to a surface of the inner layer, 50 g of the Pt—Rhsupporting ceria composite oxide and 30 g of the gamma-alumina per oneliter of the honeycomb carrier. The resulting article dried at 100° C.and baked at 500° C. to form an outer layer. Thus, an exhaust gaspurifying catalyst was produced.

The exhaust gas purifying catalyst contained 1.00 g of Pt, 0.66 g of Pd,and 0.50 g of Rh per one liter of the honeycomb carrier.

Determination Test Example 1

1) High Temperature Endurance Treatment (R/L 1000° C.)

The above prepared powdery exhaust gas purifying catalysts according toExamples and Comparative Examples shown in Table 1 were subjected tohigh temperature endurance treatment under the following relations. Inthe high temperature endurance treatment, the atmospheric temperaturewas set at 1000° C., and a cycle for a total of 30 minutes comprising aninert atmosphere for 5 minutes, an oxidative atmosphere for 10 minutes,an inert atmosphere for 5 minutes, and a reducing atmosphere for 10minutes was repeated 10 times, for a total of five hours. The aboveatmospheres were constituted by supplying gases containing hightemperature steam and having the following compositions, respectively,at a flow rate of 300 L/hr. The temperatures of the atmospheres werehold to 1000° C. by the action of high temperature steam.

Inert atmosphere gas composition: 8% of CO₂, 10% of H₂O, with thebalance of N₂

Oxidative atmosphere gas composition: 1% of O₂, 8% of CO₂, 10% of H₂O,with the balance of N₂

Reducing atmosphere gas composition: 0.5% of H₂, 1.5% of CO, 8% of CO₂,10% of H₂O, with the balance of N₂

2) High Temperature Endurance Treatment (Air 1150° C.)

The above prepared powdery exhaust gas purifying catalysts according toExamples and Comparative Examples shown in Table 1 were subjected to thehigh temperature endurance treatment in an atmosphere of the air (in anormal atmosphere).

3) Measurement of Specific Surface Area

The specific surface areas of the above prepared powdery exhaust gaspurifying catalysts according to Examples and Comparative Examples shownin Table 1 were measured before and after the high temperature endurancetreatments. The specific surface areas were measured according to theBET method. The results are shown in Table 1.

TABLE 1 Test Example 1 Specific surface area (m2/g) After Afterendurance endurance Before high After test/Before After test/BeforeExamples/ temperature endurance endurance endurance enduranceComparative endurance treatment treatment treatment treatment ExamplesComposition treatment (1000° C.) (1000° C.) (%) (1150° C.) (1150° C.)(%) Example La1.00Fe0.95Pd0.05O3/ 75.2 66.2 88.0 40.2 53.5 QA-1theta-alumina (1:3) Example La1.00Fe0.95Pd0.05O3/ 87.5 82.5 94.3 62.271.1 QA-2 La-theta-alumina (La:4%) (1:4) Example La1.00Fe0.95Pd0.05O3/51.2 46.1 90.0 35.3 68.9 QA-3 La-theta-alumina (La:4%) (1:1) ExampleLa1.00Fe0.57Mn0.38Rh0.05O3/ 96.4 91.3 94.7 71.9 74.6 QA-4La-theta-alumina (La:2%) (1:9) Example La1.00Fe0.95Rh0.05O3/ 63.2 57.390.7 43.8 69.3 QA-5 La-theta-alumina (La:10%) (2:3) ExampleLa0.95Ag0.05Fe0.57Mn0.38Pt0.05O3/ 51.1 47.2 92.4 35.5 69.5 QA-6La-theta-alumina (La:10%) (1:1) Example La0.90Ca0.10Fe0.90Pt0.10O3/ 85.477.0 90.2 58.3 68.3 QA-7 theta-alumina (1:4) ExampleLa1.00Fe0.90Pd0.10O3/ 48.7 40.3 82.8 33.6 69.0 QA-7-1 La-theta-alumina(La:4%) (1:1) Example La1.00Fe0.80Pd0.20O3/ 50.4 42.8 84.9 35.3 70.0QA-7-2 La-theta-alumina (La:4%) (1:1) Comparative La1.00Fe0.95Pd0.05O3/50.1 42.3 84.4 5.3 10.6 Example Zr0.70Ce0.25La0.02Y0.03Oxide QX-1 (1:4)Comparative La1.00Fe0.95Rh0.05O3/ 25.2 16.0 63.5 3.4 13.5 ExampleZr0.50Ce0.40La0.05Y0.05Oxide QX-2 (2:3) ComparativeLa0.90Ca0.10Fe0.90Pt0.10O3/ 43.2 35.3 81.7 3.1 7.2 ExampleZr0.70Ce0.25Pr0.02Nd0.03Oxide QX-3 (1:4) ComparativeLa1.00Fe0.95Pd0.05O3/ 140.6 101.4 72.1 43.2 30.7 Example gamma-alumina(1:4) QX-4

Test Example 2

1) Endurance Test

The exhaust gas purifying catalysts according to Examples andComparative Examples were connected to a bank of a V type eight cylinderengine of 4 liters. With the cycle shown in Tables 2 and 3 as a singlecycle (30 seconds) at 1050° C. or 1100° C., the endurance test wasrepeated for time periods shown in Tables 2 and 3. Then, annealing wascarried out at a fuel-air ratio A/F of 14.3, at 900° C. for two hours.

One cycle was set as follows. Specifically, from Second 0 to Second 5 (aperiod of 5 seconds), a mixed gas which was kept of amount oftheoretical fuel-air ratio (A/F=14.6, in the stoichiometric state) underfeedback control was fed to the engine and the internal temperature ofthe exhaust gas purifying catalysts was set at around 850° C. FromSecond 5 to Second 30 (a period of 25 seconds), the feedback wasreleased. From Second 5 to Second 7 (a period of 2 seconds), the fuelwas injected excessively, so that the fuel rich mixed gas (A/F=11.2) wasfed to the engine. From Second 7 to Second 28 (a period of 21 seconds),while an excessive amount of fuel was kept on being fed to the engine,secondary air was introduced from the upstream into the exhaust gaspurifying catalysts through an inlet tube, to cause the excessive fuelto react with the secondary air in the interior of the exhaust gaspurifying catalysts, so as to raise the temperature. In this timeperiod, the fuel-air ratio in the exhaust gas in the exhaust gaspurifying catalysts was substantially kept in a somewhat lean state thanthe stoichiometric state (A/F=14.8), and the highest temperature in thecatalyst bed was 1050° C. or 1100° C. as shown in Tables 2 and 3. FromSecond 28 to Second 30 (a period of 2 seconds), no excessive fuel wasfed to the engine but the secondary air was fed to the exhaust gaspurifying catalysts to put the exhaust gas into a lean state.

The temperatures of the exhaust gas purifying catalysts were measuredwith a thermocouple inserted into a center part of the honeycombcarrier. A phosphorus compound was added to the fuel (gasoline) so thatphosphorus element in the exhaust gas poisons the catalysts. The amountof the phosphorus compound was set so that 816 mg in terms of phosphoruselement was deposited to the exhaust gas purifying catalysts during theendurance time shown in Tables 4 to 7.

2) HC 50% Purification Temperature

The mixed gas held substantially in the stoichiometric state wassupplied to the engine. While the temperature of the exhaust gasexhausted by the combustion of the mixed gas was raised at a rate of 30°C. per minute, the exhaust gas was fed to the exhaust gas purifyingcatalysts according to Examples and Comparative Examples shown in Tables2 and 3 which had been subjected to the endurance.

The exhaust gas was fed to the exhaust gas purifying catalysts at aspace velocity SV of 90000/h. The HC level in the exhaust gas treated bythe exhaust gas purifying catalysts was measured. In this procedure, theHC 50% purification temperature was defined as the temperature at thetime when HC in the exhaust gas was purified to 50%. The results areshown in Tables 2 and 3. The mixed gas to be fed to the engine was setsubstantially in the stoichiometric state by the feed back control, andthe A/F was set at 14.6±1.0.

TABLE 2 Test Example 2 Amount Endurance HC 50% purification supportedtest temperature for (g/L) Cycling time endurance (° C.) ExamplesComposition Pt Pd Rh (hrs) 1050° C. 1100° C. ExampleLa1.00Fe0.95Pd0.05O3/ 1.50 0.33 0.40 40 — 392 RA-8 La-theta-alumina(La:4%) (1:1) (30 g) + 48 351 — Pt-Rh/Zr0.76Ce0.18La0.02Nd0.04Oxide (30g) + Pt/Ce0.60Zr0.30Y0.10Oxide (80 g) + Pt-Rh/theta-alumina (70 g)Example La1.00Fe0.95Pd0.05O3/ 1.50 0.33 0.40 40 — 423 RA-9La-theta-alumina (La:4%) (1:1) (30 g) + 48 362 —Pt/Ce0.60Zr0.30Y0.10Oxide (80 g) + Pt-Rh/gamma-alumina (70 g) ExampleLa1.00Fe0.95Pd0.05O3/ 1.50 0.33 0.40 40 — 418 RA-9-1 alpha-alumina (1:2)(45 g) + 48 365 — Pt-Rh/Zr0.76Ce0.18La0.02Nd0.04Oxide (40 g) +Pt/Ce0.60Zr0.30Y0.10Oxide (80 g) + gamma-alumina (70 g) ComparativePd/theta-alumina (30 g) + 1.50 0.33 0.40 40 — >500 ExamplePt/Ce0.60Zr0.30Y0.10Oxide (40 g) + 48 395 — RX-5 Pt-Rh/theta-alumina (60g)

TABLE 3 Test Example 2 Endurance HC 50% purification Amount supportedtest temperature for Composition (g/L) Cycling endurance (° C.) ExamplesInner layer Outer layer Pt Pd Rh time (hrs) 1050° C. 1100° C. ExampleLa1.00Fe0.95Pd0.05O3/ Pt-Rh/ 0.60 0.30 0.40 40 — 377 RC-10La-theta-alumina (La:4%) Zr0.76Ce0.18La0.02Nd0.04 48 359 — (1:1) (28g) + Oxide (30 g) + Pt/Ce0.60Zr0.30Y0.10Oxide Pt/Ce0.60Zr0.30Y0.10Oxide(60 g) + (60 g) + theta-alumina (70 g) Pt/theta-alumina (70 g) ExampleLa1.00Fe0.95Pd0.05O3/ Pt-Rh/ 0.78 0.33 0.55 40 — 368 RC-11La-theta-alumina (La:4%) Zr0.50Ce0.40La0.05Nd0.05 48 347 — (1:1) (30g) + Oxide (30 g) + Pt/Ce0.60Zr0.30Y0.10Oxide Pt/Ce0.60Zr0.30Y0.10Oxide(30 g) + (60 g) + theta-alumina (80 g) Pt-Rh/theta-alumina (70 g)Example La1.00Fe0.95Pd0.05O3/ La1.00Fe0.95Rh0.05O3/ 0.70 0.20 0.20 40 —374 RC-12 Ba-theta-alumina (Ba:4%) theta-alumina (1:3) (38 g) + 48 361 —(1:4) (46 g) + Pt/Ce0.60Zr0.30Y0.10Oxide Pt/Ce0.60Zr0.30Y0.10Oxide (60g) (45 g) Example La1.00Fe0.95Pd0.05O3/ La0.90Ca0.10Fe0.90Pt0.10O3/ 0.700.35 0.50 40 — 363 RC-13 alpha-alumina (2:3) (40 g) + theta-alumina(2:3) (3.2 g) + 48 335 — Pt/Ce0.60Zr0.30Y0.10Oxide Pt-Rh/ (30 g) +Zr0.70Ce0.25La0.02Nd0.03 theta-alumina (80 g) Oxide (40 g) +Pt/Ce0.60Zr0.30Y0.10Oxide (60 g) Comparative La1.00Fe0.95Pd0.05O3/gamma-Pt-Rh/Ce0.30Zr0.70O2 (50 g) + 1.00 0.66 0.50 48 — >500 Example alumina(1:1) (60 g) + gamma-alumina (30 g) 432 — RX-6 gamma-alumina (30 g)

While the illustrative embodiments and examples of the present inventionare provided in the above description, such is for illustrative purposeonly and it is not to be construed restrictively. Modification andvariation of the present invention which will be obvious to thoseskilled in the art is to be covered in the following claims.

INDUSTRIAL APPLICABILITY

The present invention is utilized as a method for industriallyefficiently producing an exhaust gas purifying catalyst.

1. A method for producing an exhaust gas purifying catalyst, whichcomprises the steps of: preparing a pre-crystallization compositioncontaining elementary components, the elementary components constitutinga perovskite-type composite oxide containing a noble metal; mixing thepre-crystallization composition with a powder of theta-alumina and/oralpha-alumina to prepare a mixture; and subjecting thepre-crystallization mixture to heat treatment whereby, theperovskite-type composite oxide containing the noble metal is supportedon theta-alumina and/or alpha-alumina; wherein the perovskite-typecomposite oxide is represented by the general formula (1):AB_(1-m)N_(m)O₃  (1) wherein A represents at least one element selectedfrom rare earth elements and alkaline earth metals; B represents atleast one element selected from Al and transition elements excluding therare earth elements and noble metals; N represents at least one noblemetal; and m represents an atomic ratio of N satisfying the followingrelation: 0<m<0.5; and wherein said method results in theperovskite-type composite oxide containing a noble metal supported ontheta-alumina and/or alpha-alumina, and does not include adding furthernoble metal to said theta-alumina and/or alpha-alumina.
 2. The methodfor producing an exhaust gas purifying catalyst according to claim 1,wherein N in the general formula (1) is at least one selected from thegroup consisting of Rh, Pd, and Pt.
 3. The method for producing anexhaust gas purifying catalyst according to claim 1, wherein theperovskite-type composite oxide represented by the general formula (1)is at least one selected from the group consisting of Rh containingperovskite-type composite oxides represented by the following generalformula (2), Pd containing perovskite-type composite oxides representedby the following general formula (3), and Pt containing perovskite-typecomposite oxides represented by the general formula (4):A_(1-p)A^(′) _(p)B_(1-q)Rh_(q)O₃  (2) wherein A represents at least oneelement selected from La, Nd, and Y; A′ represents Ce and/or Pr; Brepresents at least one element selected from Fe, Mn, and Al; prepresents an atomic ratio of A′ satisfying the following relation0≦p<0.5; and q represents an atomic ratio of Rh satisfying the followingrelation: 0<q≦0.8,AB_(1-r)Pd_(r)O₃  (3) wherein A represents at least one element selectedfrom La, Nd, and Y; B represents at least one element selected from Fe,Mn and Al; and r represents an atomic ratio of Pd satisfying thefollowing relation: 0<r<0.5,A_(1-s)A′_(s)B_(1-t-u)B′_(t)Pt_(u)O₃  (4) wherein A represents at leastone element selected from La, Nd, and Y; A′ represents at least oneelement selected from Mg, Ca, Sr, Ba, and Ag; B represents at least oneelement selected from Fe, Mn, and Al; B′ represents at least one elementselected from Rh and Ru; s represents an atomic ratio of A′ satisfyingthe following relation: 0<s≦0.5; t represents an atomic ratio of B′satisfying the following relation: 0≦t<0.5; and u represents an atomicratio of Pt satisfying the following relation: 0<u≦0.5.
 4. The methodfor producing an exhaust gas purifying catalyst according to claim 1,theta-alumina and/or alpha-alumina is represented by the followinggeneral formula (5):(Al_(1-g)D_(g))₂O₃  (5) wherein D represents La and/or Ba; and grepresents an atomic ratio of D satisfying the following relation:0≦g≦0.5.
 5. The method for producing an exhaust gas purifying catalystaccording to claim 1, further comprising preparing thepre-crystallization composition by mixing a solution containingalkoxides of elementary components constituting the perovskite-typecomposite oxide excluding at least one noble metal with a solutioncontaining an organometal salt of at least one noble metal.
 6. Themethod for producing an exhaust gas purifying catalyst according toclaim 5, wherein the organomatal salt of the noble metal is a noblemetal complex comprising at least one of a β-diketone compound orβ-ketoester compound represented by the following general formula (6)and/or a β-dicarboxylic ester compound represented by the followinggeneral formula (7):R³COCHR⁵COR⁴  (6) wherein R³ represents an alkyl group having 1 to 6carbon atoms, a fluoroalkyl group having 1 to 6 carbon atoms or an arylgroup; R⁴ represents an alkyl group having 1 to 6 carbon atoms, afluoroalkyl group having 1 to 6 carbon atoms, an aryl group or analkyloxy group having 1 to 4 carbon atoms; and R⁵ represents a hydrogenatom or an alkyl group having 1 to 4 carbon atoms,R⁷CH(COOR⁶)₂  (7) wherein R₆ represents an alkyl group having 1 to 6carbon atoms; and R⁷ represents a hydrogen atom or an alkyl group having1 to 4 carbon atoms.
 7. The method of claim 1, wherein thepre-crystallization composition comprises elementary components of atleast one noble metal.
 8. The method of claim 1, further comprisingmixing elementary components of at least one noble metal with thepre-crystallization composition containing elementary components ofother elementary components constituting a perovskite-type compositeoxide.
 9. The method of claim 1, further comprising mixing elementarycomponents of at least one noble metal into the mixture ofpre-crystallization composition and theta-alumina and/or alpha-alumina.